Power output apparatus and hybrid vehicle with power output apparatus

ABSTRACT

A hybrid vehicle  20  of the invention is equipped with a power distribution integration mechanism  40  and a transmission  60 . The power distribution integration mechanism  40  is a double pinion planetary gear mechanism constructed to include a carrier  45  connecting with a motor MG 2 , a sun gear  41  connecting with a motor MG 1 , and a ring gear  42  connecting with an engine  22  and to have a gear ratio of approximately 0.5. The transmission  60  includes a three element-type first change speed planetary gear mechanism PG 1 , a three element-type second change speed planetary gear mechanism PG 2 , a brake clutch BC 1  configured to fix a ring gear  62  of the first change speed planetary gear mechanism PG 1  in a non-rotatable manner and release the ring gear  62  in a rotatable manner, and a brake clutch BC 2  configured to enable and disable power transmission via the second change speed planetary gear mechanism PG 2.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power output apparatus configured tooutput power to a driveshaft and to a hybrid vehicle equipped with sucha power output apparatus.

2. Description of the Prior Art

One proposed structure of the power output apparatus includes aninternal combustion engine, two motors, a Ravigneaux planetary gearmechanism, and a parallel shaft-type transmission arranged toselectively link an output member with one of two output elements of theplanetary gear mechanism respectively connected to the motors (see, forexample, Japanese Patent Laid-Open No. 2005-155891). Another proposedstructure of the power output apparatus includes a planetary gearmechanism having an input element connected to an internal combustionengine and two output elements respectively connected to motors, and aparallel shaft-type transmission including two countershaftsrespectively connected to the corresponding output elements of theplanetary gear mechanism and linked with an output shaft (see, forexample, Japanese Patent Laid-Open No. 2003-106389). In these prior artpower output apparatuses, the parallel shaft-type transmission switchesover the output element of the planetary gear mechanism to be linkedwith the output member or with the output shaft.

Because of the limited space for mounting the power output apparatus,there is a difficulty in application of the power output apparatus inthe former cited reference to a vehicle having a rear wheel-drive systemas a main drive system, that is, a rear wheel-drive vehicle or a rearwheel drive-based four wheel drive vehicle. The power output apparatusin the latter cited reference is applicable to the rear wheel-drivevehicle. The parallel shaft-type transmission, however, has rather largedimensions both in an axial direction and in a radial direction and isthus not suitable for mounting on the vehicle. The power outputapparatus in the latter cited reference also requires a rotor of a largediameter and thereby causes its electrical drive system to be ratherbulky and unsuitable for mounting on the vehicle. Moreover the poweroutput apparatus in the latter cited reference has the low possibilityfor the practical application. In application of the power outputapparatus in the latter cited reference to the vehicle having the rearwheel-drive system as the main drive system, a further improvement ofthe power transmission efficiency is required in a wider drive range.There is thus still room for improvement in the power output apparatusesof these prior art structures.

SUMMARY OF THE INVENTION

There would thus be a demand for size reduction of the power outputapparatus to be favorably mounted on a vehicle and especially suitablefor a vehicle having a rear wheel drive system as a main drive system.In the power output apparatus and the hybrid vehicle equipped with thepower output apparatus, there would also be a demand for improvement ofpower transmission efficiency in a wide drive range.

The present invention accomplishes at least part of the demandsmentioned above by the following configurations applied to the poweroutput apparatus and to the hybrid vehicle with the power outputapparatus.

According to one aspect, the invention is directed to a power outputapparatus configured to output power to a driveshaft. The power outputapparatus includes: an internal combustion engine; a first motor capablepower input and power output; a second motor capable power input andpower output; an accumulator configured to transmit electric power toand from the first motor and the second motor; a power distributionintegration mechanism being a planetary gear mechanism including a firstelement connecting with a rotating shaft of the first motor, a secondelement connecting with a rotating shaft of the second motor, and athird element connecting with an engine shaft of the internal combustionengine, and configured to allow mutually differential rotations of thethree elements and to have a gear ratio of approximately 0.5; and achange speed transmission assembly. The change speed transmissionassembly includes: a first change speed planetary gear mechanism havingan input element connecting with the first element of the powerdistribution integration mechanism, an output element connecting withthe driveshaft, and a fixable element and configured to allow mutuallydifferential rotations of the three elements; a first fixation deviceconfigured to fix the fixable element of the first change speedplanetary gear mechanism in a non-rotatable manner and to release thefixable element in a rotatable manner; a second change speed planetarygear mechanism having an input element connecting with the secondelement of the power distribution integration mechanism, an outputelement connecting with the driveshaft, and a fixable element andconfigured to allow mutually differential rotations of the threeelements; and a transmission state changeover device configured tochange over a state of either one of the input element and the fixableelement of the second change speed planetary gear mechanism and therebyenable and disable power transmission via the second change speedplanetary gear mechanism.

The power output apparatus according to one aspect of the invention isequipped with the power distribution integration mechanism constructedas the three element-type planetary gear mechanism having a gear ratioof approximately 0.5. The power distribution integration mechanism ofthis structure is small-sized and enables the first motor and the secondmotor to have identical specifications without requiring a reductiongear mechanism or any equivalent mechanism. This arrangement thuscontributes to size reduction of the power output apparatus. The poweroutput apparatus is also equipped with the change speed transmissionassembly including the three-element-type first change speed planetarygear mechanism and the three-element-type second change speed planetarygear mechanism. The change speed transmission assembly is arrangedcoaxially with and in the downstream of the internal combustion engine,the first motor, the second motor, and the power distributionintegration mechanism. The change speed transmission assembly of thisarrangement enables size reduction both in its axial direction and inits radial direction, compared with the parallel shaft-type change speedtransmission assembly. The combination of the power distributionintegration mechanism constructed as the three element-type planetarygear mechanism having the gear ratio of approximately 0.5 with thechange speed transmission assembly including the three element-typefirst change speed planetary gear mechanism and the three element-typesecond change speed planetary gear mechanism desirably downsizes thepower output apparatus to be extremely favorable for mounting on thevehicle having a rear wheel drive system as a main drive system. In onestate of the change speed transmission assembly, the first fixationstructure is set to fix the fixable element of the first change speedplanetary gear mechanism in the non-rotatable manner, while thetransmission state changeover structure is set to disable the powertransmission via the second change speed planetary gear mechanism. Suchsetting causes the first element of the power distribution integrationmechanism to work as the output element and enables the first motorconnecting with the first element to function as the motor, whileenabling the second motor connecting with the second element working asthe reactive element to function as the generator. In another state ofthe change speed transmission assembly, the first fixation structure isset to release the fixable element of the first change speed planetarygear mechanism in the rotatable manner and thereby disable the powertransmission via the first change speed planetary gear mechanism, whilethe transmission state changeover structure is set to enable the powertransmission via the second change speed planetary gear mechanism. Suchsetting causes the second element of the power distribution integrationmechanism to work as the output element and enables the second motorconnecting with the second element to function as the motor, whileenabling the first motor connecting with the first element working asthe reactive element to function as the generator. In the power outputapparatus according to this aspect of the invention, the first fixationstructure and the transmission state changeover structure are adequatelycontrolled to prevent the occurrence of power circulation that istriggered by a negative rotation speed of the second motor or the firstmotor functioning as the generator in response to an increase inrotation speed of the first motor or the second motor functioning as themotor. In another state of the change speed transmission assembly, thefirst fixation structure is set to fix the fixable element of the firstchange speed planetary gear mechanism in the non-rotatable manner, whilethe transmission state changeover structure is set to enable the powertransmission via the second change speed planetary gear mechanism. Suchsetting enables the power of the internal combustion engine to bemechanically (directly) transmitted to the driveshaft at a fixed changegear ratio. The power output apparatus of this arrangement effectivelyimproves the power transmission efficiency in a wide drive range. Thegear ratio of approximately 0.5 may be selected in a range of 0.4 to0.6.

In one preferable embodiment according to one aspect of the invention,the power distribution integration mechanism may be a double pinionplanetary gear mechanism including a ring gear as the third element, asun gear as the second element, and a carrier as the first elementarranged to hold sets of two pinion gears engaging with each other, oneof the two pinion gears engaging with the ring gear and the other of thetwo pinion gears engaging with the sun gear. The power distributionintegration mechanism constructed as the double pinion planetary gearmechanism having the gear ratio of approximately 0.5 has a smaller outerdiameter and accordingly enables further size reduction of the poweroutput apparatus.

In one preferable application of the power output apparatus, the fixableelement of the second change speed planetary gear mechanism may be fixedin the non-rotatable manner, and the transmission state changeoverdevice may be a coupling-decoupling device configured to couple anddecouple the second element of the power distribution integrationmechanism with and from the input element of the second change speedplanetary gear mechanism. The transmission state changeover structuremay be configured to enable and disable the power input into the secondchange speed planetary gear mechanism.

In one preferable embodiment of the power output apparatus of the aboveapplication, the change speed transmission assembly may further includea coupling device configured to couple and decouple the output elementwith and from the fixable element of the first change speed planetarygear mechanism. In one state of the change speed transmission assemblyof this structure, while the transmission state changeover structure isset to enable the power transmission via the second change speedplanetary gear mechanism, the coupling structure is set to couple theoutput element with the fixable element of the first change speedplanetary gear mechanism. Such setting enables the power of the internalcombustion engine to be mechanically (directly) transmitted to thedriveshaft at a fixed change gear ratio, which is different from thefixed change gear ratio in the state of fixing the fixable element ofthe first change speed planetary gear mechanism in the non-rotatablemanner by means of the first fixation structure and enabling the powertransmission via the second change speed planetary gear mechanism bymeans of the transmission state changeover structure. In this state,setting the transmission state changeover structure to disable the powertransmission via the second change speed planetary gear mechanism causesthe coupling structure to substantially lock and integrally rotate therespective elements of the first change speed planetary gear mechanism.Such setting enables direct transmission of the power from the firstelement of the power distribution integration mechanism to thedriveshaft. This arrangement ensures the enhanced power transmissionefficiency in a wider drive range.

In the power output apparatus of the above embodiment, the change speedtransmission assembly may include one single clutch functioning both asthe first fixation device and as the coupling device. This arrangementeffectively downsizes the change speed transmission assembly and thewhole power output apparatus, while simplifying their configurations.

In another preferable application of the power output apparatus, thetransmission state changeover device may be a second fixation deviceconfigured to fix the fixable element of the second change speedplanetary gear mechanism in a non-rotatable manner and to release thefixable element in a rotatable manner. The transmission state changeoverstructure may be configured to fix the fixable element in thenon-rotatable manner and thereby enable the power transmission via thesecond change speed planetary gear mechanism and to release the fixableelement in the rotatable manner and thereby disable the powertransmission via the second change speed planetary gear mechanism.

In one preferable embodiment of the power output apparatus of the aboveapplication, the change speed transmission assembly may further includea first coupling device configured to couple and decouple the outputelement with and from the fixable element of the first change speedplanetary gear mechanism, and a second coupling device configured tocouple and decouple the output element with and from the fixable elementof the second change speed planetary gear mechanism. In one state of thechange speed transmission assembly of this structure, the transmissionstate changeover structure is set to enable the power transmission viathe second change speed planetary gear mechanism, while the firstcoupling structure is set to couple the output element with the fixableelement of the first change speed planetary gear mechanism. Such settingenables the power of the internal combustion engine to be mechanically(directly) transmitted to the driveshaft at a fixed change gear ratio,which is different from the fixed change gear ratio in the state offixing the fixable element of the first change speed planetary gearmechanism in the non-rotatable manner by means of the first fixationstructure and enabling the power transmission via the second changespeed planetary gear mechanism by means of the transmission statechangeover structure. In this state, setting the transmission statechangeover structure to disable the power transmission via the secondchange speed planetary gear mechanism causes the first couplingstructure to substantially lock and integrally rotate the respectiveelements of the first change speed planetary gear mechanism. Suchsetting enables direct transmission of the power from the first elementof the power distribution integration mechanism to the driveshaft. Inanother state of the change speed transmission assembly, the firstcoupling structure is set to couple the output element with the fixableelement of the first change speed planetary gear mechanism, while thesecond coupling structure is set to couple the output element with thefixable element of the second change speed planetary gear mechanism.Such setting causes the respective elements of the power distributionintegration mechanism and the respective elements of the first and thesecond change speed planetary gear mechanisms to be integrally rotated.Such setting enables the power of the internal combustion engine to bemechanically (directly) transmitted to the driveshaft at a fixed changegear ratio of 1, which is different from the fixed change gear ratio inthe state of fixing the fixable element of the first change speedplanetary gear mechanism in the non-rotatable manner and enabling thepower transmission via the second change speed planetary gear mechanismby means of the transmission state changeover structure and from thefixed change gear ratio in the state of enabling the power transmissionvia the second change speed planetary gear mechanism and coupling theoutput element with the fixable element of the first change speedplanetary gear mechanism by means of the first coupling structure. Thisarrangement ensures the enhanced power transmission efficiency in awider drive range.

In the power output apparatus of the above embodiment, the change speedtransmission assembly may include one single first clutch functioningboth as the first fixation device and as the first coupling device andone single second clutch functioning both as the second fixation deviceand as the second coupling device. This arrangement effectivelydownsizes the change speed transmission assembly and the whole poweroutput apparatus, while simplifying their configurations.

The power output apparatus may further include: a third fixation deviceconfigured to fix either one of the first element and the second elementof the power distribution integration mechanism in a non-rotatablemanner. The non-rotatable fixation of either the first element or thesecond element (reactive element) of the power distribution integrationmechanism connecting with the first motor or with the second motorfunctioning as the generator in the state of coupling the output elementwith the fixable element in either of the first change speed planetarygear mechanism and the second change speed planetary gear mechanismenables the power of the internal combustion engine to be mechanically(directly) transmitted to the driveshaft at a fixed change gear ratio ofless than 1 intrinsic to this state. This arrangement desirably improvesthe power transmission efficiency in a wider drive range.

In one preferable embodiment of the power output apparatus according tothe above aspect of the invention, the first change speed planetary gearmechanism may be a single pinion planetary gear mechanism including asun gear as the input element, a ring gear as the fixable element, and acarrier as the output element arranged to hold pinion gears respectivelyengaging with both the sun gear and the ring gear, and the second changespeed planetary gear mechanism may be a single pinion planetary gearmechanism including a ring gear as the input element, a sun gear as thefixable element, and a carrier as the output element arranged to holdpinion gears respectively engaging with both the ring gear and the sungear. The first and the second change speed planetary gear mechanismsconstructed as the single pinion planetary gear mechanisms effectivelydownsizes the change speed transmission assembly and the whole poweroutput apparatus.

In one preferable application of the power output apparatus of thisembodiment, the sun gear of the second change speed planetary gearmechanism may be attached to a hollow sun gear shaft, and the ring gearof the second change speed planetary gear mechanism may be connectedwith the second element of the power distribution integration mechanismvia a shaft located in and passed through the hollow sun gear shaft. Thering gear as the input element of the second change speed planetary gearmechanism is connectable with the second element of the powerdistribution integration mechanism, while the sun gear as the fixableelement of the second change speed planetary gear mechanism is fixablein the non-rotatable manner.

In another preferable application of the power output apparatus of thisembodiment, the sun gear of the second change speed planetary gearmechanism may be attached to a hollow sun gear shaft, and the carrier ofthe second change speed planetary gear mechanism may be connected withdriveshaft via a shaft located in and passed through the hollow sun gearshaft. The ring gear as the input element is connectable with the secondelement of the power distribution integration mechanism, while the sungear as the fixable element of the second change speed planetary gearmechanism is fixable in the non-rotatable manner.

In another preferable embodiment of the power output apparatus accordingto the above aspect of the invention, the first change speed planetarygear mechanism may be a single pinion planetary gear mechanism includinga sun gear as the input element, a ring gear as the fixable element, anda carrier as the output element arranged to hold pinion gearsrespectively engaging with both the sun gear and the ring gear, and thesecond change speed planetary gear mechanism may be a planetary gearmechanism including a first sun gear as the input element, a second sungear as the output element having a different number of teeth from thatof the first sun gear and connected with the carrier of the first changespeed planetary gear mechanism and with the driveshaft, and a carrier asthe fixable element arranged to hold a stepped gear of linking a firstpinion gear engaging with the first sun gear to a second pinion gearengaging with the second sun gear. The second change speed planetarygear mechanism constructed as the planetary gear mechanism including thestepped gear has a smaller dimension in its radial direction, thusenabling size reduction of the change speed transmission assemblyespecially in the radial direction.

In still another preferable embodiment of the power output apparatusaccording to the above aspect of the invention, the first change speedplanetary gear mechanism may be a single pinion planetary gear mechanismincluding a sun gear as the input element, a ring gear as the fixableelement, and a carrier as the output element arranged to hold piniongears respectively engaging with both the sun gear and the ring gear,and the second change speed planetary gear mechanism may be a doublepinion planetary gear mechanism including a sun gear as the inputelement, a ring gear as the output element, and a carrier as the fixableelement arranged to hold sets of two pinion gears engaging with eachother, one of the two pinion gears engaging with the sun gear and theother of the two pinion gears engaging with the ring gear.

According to another aspect, the invention is directed to a hybridvehicle with drive wheels driven by means of power from a driveshaft.The hybrid vehicle includes: an internal combustion engine; a firstmotor capable power input and power output; a second motor capable powerinput and power output; an accumulator configured to transmit electricpower to and from the first motor and the second motor; a powerdistribution integration mechanism being a planetary gear mechanismincluding a first element connecting with a rotating shaft of the firstmotor, a second element connecting with a rotating shaft of the secondmotor, and a third element connecting with an engine shaft of theinternal combustion engine, and configured to allow mutuallydifferential rotations of the three elements and to have a gear ratio ofapproximately 0.5; and a change speed transmission assembly. The changespeed transmission assembly includes: a first change speed planetarygear mechanism having an input element connecting with the first elementof the power distribution integration mechanism, an output elementconnecting with the driveshaft, and a fixable element and configured toallow mutually differential rotations of the three elements; a firstfixation device configured to fix the fixable element of the firstchange speed planetary gear mechanism in a non-rotatable manner and torelease the fixable element in a rotatable manner; a second change speedplanetary gear mechanism having an input element connecting with thesecond element of the power distribution integration mechanism, anoutput element connecting with the driveshaft, and a fixable element andconfigured to allow mutually differential rotations of the threeelements; and a transmission state changeover device configured tochange over a state of either one of the input element and the fixableelement of the second change speed planetary gear mechanism and therebyenable and disable power transmission via the second change speedplanetary gear mechanism.

The power output apparatus mounted on the hybrid vehicle is downsized tobe especially suitable for the vehicle having a rear wheel drive systemas a main drive system and is arranged to improve the power transmissionefficiency in a wide drive range. The hybrid vehicle according to theabove aspect of the invention accordingly has the enhanced fuelefficiency and the improved driving performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the configuration of a hybrid vehicle20 in one embodiment of the invention;

FIG. 2 shows the schematic structure of a transmission 60 included inthe hybrid vehicle 20 of the embodiment;

FIG. 3 shows torque-rotation speed dynamics of primary elements includedin a power distribution integration mechanism 40 and in the transmission60 in one change speed state in the transmission 60 during a drive ofthe hybrid vehicle 20 with engagement of a clutch C0 and operation of anengine 22;

FIG. 4 shows torque-rotation speed dynamics in another change speedstate;

FIG. 5 shows torque-rotation speed dynamics in another change speedstate;

FIG. 6 shows torque-rotation speed dynamics in another change speedstate;

FIG. 7 shows torque-rotation speed dynamics in another change speedstate;

FIG. 8 shows torque-rotation speed dynamics in another change speedstate;

FIG. 9 is an alignment chart showing torque-rotation speed dynamics ofrespective elements in the power distribution integration mechanism 40in a state of operating a motor MG1 as a generator and a motor MG2 as amotor;

FIG. 10 is an alignment chart showing torque-rotation speed dynamics ofthe respective elements in the power distribution integration mechanism40 in a state of operating the motor MG2 as a generator and the motorMG1 as a motor;

FIG. 11 shows a motor drive mode of the hybrid vehicle 20;

FIG. 12 shows settings of clutch positions of brake clutches BC1 and BC2and the clutch C0 during a drive of the hybrid vehicle 20; and

FIG. 13 shows the schematic structure of another transmission 60A in onemodified example;

FIG. 14 shows the schematic structure of still another transmission 60Bin another modified example;

FIG. 15 shows settings of clutch positions of brake clutches BC1 andBC2′, a brake B3, and the clutch C0 during a drive of the hybrid vehicle20 equipped with the transmission 60B including the brake clutch BC2′;

FIG. 16 shows torque-rotation speed dynamics of primary elementsincluded in the power distribution integration mechanism 40 and thetransmission 60B in an equal rotation transmission state;

FIG. 17 shows the schematic structure of another transmission 100 inanother modified example;

FIG. 18 shows the schematic structure of another transmission 100A inanother modified example;

FIG. 19 shows the schematic structure of another transmission 200 inanother modified example; and

FIG. 20 shows the schematic structure of another transmission 200A inanother modified example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some modes of carrying out the invention are described below withreference to the accompanied drawings.

FIG. 1 schematically illustrates the configuration of a hybrid vehicle20 in one embodiment of the invention. The hybrid vehicle 20 shown inFIG. 1 is constructed as a rear-wheel drive vehicle and includes anengine 22 located in a front portion of the vehicle body, a powerdistribution integration mechanism 40 connected to a crankshaft 26 ofthe engine 22, a motor MG1 linked with the power distributionintegration mechanism 40 and arranged to have power generationcapability, a motor MG2 linked with the power distribution integrationmechanism 40 and arranged to be coaxial with the motor MG1 and havepower generation capability, a transmission 60 arranged to convert theoutput power of the power distribution integration mechanism 40 andtransmit the converted power to a driveshaft 69, and a hybrid electroniccontrol unit (hereafter referred to as ‘hybrid ECU’) 70 configured tocontrol the operations of the whole hybrid vehicle 20.

The engine 22 is an internal combustion engine that receives a supply ofa hydrocarbon fuel, such as gasoline or light oil, and outputs power.The engine 22 is under control of an engine electronic control unit(hereafter referred to as ‘engine ECU’) 24 and is subjected to, forexample, fuel injection control, ignition control, and intake aircontrol. The engine ECU 24 inputs diverse signals from various sensorsthat are provided for the engine 22 to measure and detect the operatingconditions of the engine 22, for example, a crank position sensor (notshown) attached to the crankshaft 26. The engine ECU 24 establishescommunication with the hybrid ECU 70 to drive and control the engine 22in response to control signals from the hybrid ECU 70 and with referenceto the diverse signals from the various sensors and to output dataregarding the operating conditions of the engine 22 to the hybrid ECU 70according to the requirements.

The motors MG1 and MG2 are constructed as synchronous motor generatorsof an identical specification that may be actuated both as a generatorand as a motor. The motors MG1 and MG2 transmit electric power to andfrom a battery 35 as a secondary cell via inverters 31 and 32. Powerlines 39 connecting the battery 35 with the inverters 31 and 32 arestructured as common positive bus and negative bus shared by theinverters 31 and 32. Such connection enables electric power generated byone of the motors MG1 and MG2 to be consumed by the other motor MG2 orMG1. The battery 35 may thus be charged with surplus electric powergenerated by either of the motors MG1 and MG2, while being discharged tosupplement insufficient electric power. The battery 35 is neithercharged nor discharged upon the balance of the input and output ofelectric powers between the motors MG1 and MG2. Both the motors MG1 andMG2 are driven and controlled by a motor electronic control unit(hereafter referred to as ‘motor ECU’) 30. The motor ECU 30 inputsvarious signals required for driving and controlling the motors MG1 andMG2, for example, signals representing rotational positions of rotors inthe motors MG1 and MG2 from rotational position detection sensors 33 and34 and signals representing phase currents to be applied to the motorsMG1 and MG2 from current sensors (not shown). The motor ECU 30 outputsswitching control signals to the inverters 31 and 32. The motor ECU 30executes a rotation speed computation routine (not shown) to computerotation speeds Nm1 and Nm2 of the rotors in the motors MG1 and MG2 fromthe signals output from the rotational position detection sensors 33 and34. The motor ECU 30 establishes communication with the hybrid ECU 70 todrive and control the motors MG1 and MG2 in response to control signalsreceived from the hybrid ECU 70 and to output data regarding theoperating conditions of the motors MG1 and MG2 to the hybrid ECU 70according to the requirements.

The battery 35 is under control and management of a battery electroniccontrol unit (hereafter referred to as ‘battery ECU’) 36. The batteryECU 36 inputs various signals required for management and control of thebattery 35, for example, an inter-terminal voltage from a voltage sensor(not shown) located between terminals of the battery 35, acharge-discharge current from a current sensor (not shown) located inthe power line 39 connecting with an output terminal of the battery 35,and a battery temperature Tb from a temperature sensor 37 attached tothe battery 35. The battery ECU 36 outputs data regarding the operatingconditions of the battery 35 by communication to the hybrid ECU 70 andto the engine ECU 24 according to the requirements. In the structure ofthis embodiment, the battery ECU 36 computes a remaining charge level orcurrent state of charge SOC of the battery 35 from integration of thecharge-discharge current measured by the current sensor and calculates acharge-discharge power demand Pb* of the battery 35 from the computedstate of charge SOC. The battery ECU 36 also sets an input limit Win asan allowable charging power to be charged into the battery 35 and anoutput limit Wout as an allowable discharging power to be dischargedfrom the battery 35, based on the computed state of charge SOC and themeasured battery temperature Tb. A concrete procedure of setting theinput limit Win and the output limit Wout of the battery 35 sets basevalues of the input limit Win and the output limit Wout corresponding tothe battery temperature Tb, specifies an input limit correction factorand an output limit correction factor corresponding to the state ofcharge SOC of the battery 35, and multiplies the base values of theinput limit Win and the output limit Wout by the specified input limitcorrection factor and output limit correction factor to determine theinput limit Win and the output limit Wout of the battery 35.

The power distribution integration mechanism 40 is provided with themotors MG1 and MG2 and the transmission 60 in a non-illustratedtransmission case (casing) and is arranged apart from the engine 22 by apredetermined distance to be coaxial with the crankshaft 26. The powerdistribution integration mechanism 40 of the embodiment is constructedas a double pinion planetary gear mechanism and includes a sun gear 41as an external gear, a ring gear 42 as an internal gear arrangedconcentrically with the sun gear 41, and a carrier 45 arranged tosupport at least one set of two intermeshing pinion gears 43 and 44 suchas to allow both their revolutions and their rotations on their axes,where one of the two intermeshing pinion gears 43 and 44 engages withthe sun gear 41 and the other engages with the ring gear 42. In thispower distribution integration mechanism 40, the sun gear 41 (secondelement), the ring gear 42 (third element), and the carrier 45 (firstelement) are designed as elements of differential rotations. The sungear 41 as the second element of the power distribution integrationmechanism 40 is connected with the motor MG1 (more specifically with itshollow rotor) as a second motor via a hollow sun gear shaft 41 aextended from the sun gear 41 in a direction opposite to the engine 22(that is, in a rearward direction of the vehicle body) and a hollowfirst motor shaft 46. The carrier 45 as the first element is connectedwith the motor MG2 (more specifically with its hollow rotor) as a firstmotor via a hollow second motor shaft 55 extended toward the engine 22.The ring gear 42 as the third element is connected with the crankshaft26 of the engine 22 via a ring gear shaft 42 a extended to pass throughthe second motor shaft 55 and the motor MG2, as well as a damper 28. Inthe structure of this embodiment, the power distribution integrationmechanism 40 is constructed to have a gear ratio ρ (division of thenumber of teeth of the sun gear 41 by the number of teeth of the ringgear 42) satisfying an equation of ρ=0.5. Since the sun gear 41 and thecarrier 45 have equal torque distribution fractions from the engine 22,the motors MG1 and MG2 are enabled to have identical specificationswithout using a reduction gear mechanism or any equivalent mechanism.This arrangement desirably downsizes the power output apparatus,improves the productivity of the power output apparatus, and reduces themanufacturing cost of the power output apparatus. The gear ratio ρ ofthe power distribution integration mechanism 40 may otherwise beselected in a preset range of, for example, 0.4 to 0.6.

As shown in FIG. 1, a clutch C0 (coupling-decoupling structure) isprovided between the sun gear shaft 41 a and the first motor shaft 46 toallow and release coupling (coupling of driving source elements) betweenthe sun gear shaft 41 a and the first motor shaft 46. In thisembodiment, the clutch C0 may be constructed, for example, as a dogclutch including a movable engaging member, which is moved back andforth in an axial direction of the sun gear shaft 41 a and the firstmotor shaft 46 by means of an electromagnetic, electric, or hydraulicactuator 90 to be engageable both with a mating engagement elementfastened to the sun gear shaft 41 a and with a mating engagement elementfastened to the first motor shaft 46. In response to release of thecoupling between the sun gear shaft 41 a and the first motor shaft 46 bythe clutch C0, the motor MG1 as the second motor is disconnected fromthe sun gear 41 as the second element of the power distributionintegration mechanism 40. The function of the power distributionintegration mechanism 40 thus substantially separates the engine 22 fromthe motors MG1 and MG2 and the transmission 60. The first motor shaft 46linkable with the sun gear 41 of the power distribution integrationmechanism 40 via the clutch C0 is further extended from the motor MG1 inthe direction opposite to the engine 22 (toward the rear portion of thevehicle body) and is connected with the transmission 60. A carrier shaft(coupling shaft) 45 a is extended from the carrier 45 of the powerdistribution integration mechanism 40 in the direction opposite to theengine 22 (toward the rear portion of the vehicle body) to pass throughthe hollow sun gear shaft 41 a and the hollow first motor shaft 46. Thecarrier shaft 45 a is accordingly connected with the transmission 60. Inthe structure of the embodiment, the power distribution integrationmechanism 40 is arranged coaxially with the motors MG1 and MG2 and islocated between the motors MG1 and MG2 of a mutually coaxialarrangement. The engine 22 is arranged coaxially with the motor MG2 andis located to face the transmission 60 across the power distributionintegration mechanism 40. The engine 22, the motor MG2, the powerdistribution integration mechanism 40, the motor MG1, and thetransmission 60 as the constituents of the power output apparatus arethus arranged in this sequence from the forward to the rearward of thevehicle body. This arrangement reduces the size of the power outputapparatus to be suitable for mounting on the hybrid vehicle 20 having arear wheel drive system as a main drive system.

The transmission 60 is a planetary gear-type automatic transmissionconstructed to change the speed (gear ratio) at multiple differentstages. The transmission 60 includes a first change speed planetary gearmechanism PG1 (first change speed differential rotation mechanism)connected via the carrier shaft 45 a with the carrier 45 as the firstelement of the power distribution integration mechanism 40, a secondchange speed planetary gear mechanism PG2 (second change speeddifferential rotation mechanism) connected with the first motor shaft46, which is connectable via the clutch C0 with the sun gear 41 as thesecond element of the power distribution integration mechanism 40, abrake clutch BC1 (first fixation structure and first coupling structure)provided corresponding to the first change speed planetary gearmechanism PG1, a brake clutch BC2 (transmission state changeover deviceand third fixation structure). The respective constituent elements ofthe first change speed planetary gear mechanism PG1, the second changespeed planetary gear mechanism PG2, the brake clutches BC1 and BC2 areall located inside the transmission case of the transmission 60.

As shown in FIGS. 1 and 2, the first change speed planetary gearmechanism PG1 is constructed as a single pinion planetary gear mechanismand includes a sun gear 61 (input element) connected with the carriershaft 45 a, a ring gear 62 (fixable element) as an internal geararranged coaxially with the sun gear 61, and a carrier 64 (outputelement) arranged to hold multiple pinion gears 63 engaging with boththe sun gear 61 and the ring gear 62 and linked with the driveshaft 69.The sun gear 61, the ring gear 62, and the carrier 64 are designed aselements of differential rotations. The second change speed planetarygear mechanism PG2 is also constructed as a single pinion planetary gearmechanism and includes a sun gear 65 (fixable element), a ring gear 66(input element) as an internal gear arranged coaxially with the sun gear65, and the common carrier 64 (output element) arranged to hold multiplepinion gears 67 engaging with both the sun gear 65 and the ring gear 66and shared with the first change speed planetary gear mechanism PG1. Thesun gear 65, the ring gear 66, and the carrier 64 are designed aselements of differential rotations. In the structure of this embodiment,the second change speed planetary gear mechanism PG2 is arranged to becoaxial with and ahead of the first change speed planetary gearmechanism PG1 in the vehicle body. The sun gear 65 of the second changespeed planetary gear mechanism PG2 is attached to a hollow sun gearshaft 65 a fastened to the transmission case by means of a supportmember 65 y. The sun gear 65 as the fixable element is thus continuouslyfixed in a non-rotatable manner. A hollow ring gear shaft 66 a islocated in and passed through the hollow sun gear shaft 65 a. The ringgear 66 is attached to the ring gear shaft 66 a at a position rearwardof the sun gear 65 and the pinion gear 67 but forward of the firstchange speed planetary gear mechanism PG1 in the vehicle body. Thecarrier 64 is formed to be extended from outside of the ring gear 66 andgo around to the forward of the pinion gears 67. The carrier shaft 45 ais arranged to pass through the first motor shaft 46 and the ring gearshaft 66 a. The sun gear 61 of the first change speed planetary gearmechanism PG1 is fastened to the end of the carrier shaft 45 a extendedfrom the ring gear shaft 66 a.

The brake clutch BC1 is constructed as a dog clutch including a movableengaging member EM1 and an electromagnetic, electric, or hydraulicactuator 91 to move the movable engagement member EM1 back and forth inthe axial direction of the carrier shaft 45 a. The movable engagingmember EM1 is designed to continuously engage with a mating engagementelement 62 a provided on a circumferential portion of the ring gear 62of the first change speed planetary gear mechanism PG1 and to beengageable both with a lock element 68 a fixed to the transmission caseand with a mating engagement element 64 a provided on a circumferentialportion of the carrier 64. As shown in FIG. 2, the brake clutch BC1 isstructured to selectively change over the clutch position or theposition of the movable engaging member EM1 between multiple options ‘Rposition’, ‘M position’, and ‘L position’. At the setting of the clutchposition of the brake clutch BC1 to the R position, the movable engagingmember EM1 engages with both the engagement element 62 a of the ringgear 62 and the lock element 68 a fixed to the transmission case. Suchsetting enables the ring gear 62 as the fixable element of the firstchange speed planetary gear mechanism PG1 to be fastened to thetransmission case in a non-rotatable manner. At the setting of theclutch position of the brake clutch BC1 to the M position, the movableengaging member EM1 engages with only the engagement element 62 a of thering gear 62. Such setting releases the ring gear 62 of the first changespeed planetary gear mechanism PG1 in a rotatable manner. At the settingof the clutch position of the brake clutch BC1 to the L position, themovable engaging member EM1 engages with both the engagement element 62a of the ring gear 62 and the engagement element 64 a of the carrier 64.Such setting enables the ring gear 62 as the fixable element to becoupled with the carrier 64 as the output element in the first changespeed planetary gear mechanism PG1. The brake clutch BC2 is alsoconstructed as a dog clutch including a movable engaging member EM2 andan electromagnetic, electric, or hydraulic actuator 92 to move themovable engagement member EM2 back and forth in the axial direction ofthe first motor shaft 46. The movable engaging member EM2 is designed tocontinuously engage with a mating engagement element 46 b provided onone end of the first motor shaft 46 (right end in the drawing) and to beengageable both with an engagement element 66 b provided on one end ofthe ring gear shaft 66 a (left end in the drawing) and a lock element 68b fixed to the transmission case. As shown in FIG. 2, the brake clutchBC2 is also structured to selectively change over the clutch position orthe position of the movable engaging member EM2 between multiple options‘R position’, ‘M position’, and ‘L position’. At the setting of theclutch position of the brake clutch BC2 to the R position, the movableengaging member EM2 engages with both the engagement element 46 b of thefirst motor shaft 46 and the engagement element 66 b of the ring gearshaft 66 a. Such setting enables the ring gear 66 of the second changespeed planetary gear mechanism PG2 to be coupled with the sun gear 41 asthe second element of the power distribution integration mechanism 40via the ring gear shaft 66 a, the first motor shaft 46, and the clutchC0. At the setting of the clutch position of the brake clutch BC2 to theM position, the movable engaging member EM2 engages with only theengagement element 46 b of the first motor shaft 46. Such settingdecouples the sun gear 41 of the power distribution integrationmechanism 40 from the ring gear 66 of the second change speed planetarygear mechanism PG2. At the setting of the clutch position of the brakeclutch BC2 to the L position, the movable engaging member EM2 engageswith both the engagement element 46 b of the first motor shaft 46 andthe lock element 68 b fixed to the transmission case. In the engagedstate of the first motor shaft 46 or the clutch C0, such setting fastensthe sun gear 41 of the power distribution integration mechanism 40 tothe transmission case in a non-rotatable manner.

The power transmitted from the carrier 64 of the transmission 60 to thedriveshaft 69 is eventually output through a differential gear DF torear wheels RWa and RWb as drive wheels. The transmission 60 of theabove structure enables significant size reduction both in the axialdirection and in a radial direction, compared with the parallelshaft-type transmission. The first change speed planetary gear mechanismPG1 and the second change speed planetary gear mechanism PG2 arearranged coaxially with and in the downstream of the engine 22, themotors MG1 and MG2, and the power distribution integration mechanism 40.The transmission 60 constructed as described above desirably simplifiesthe bearing structure and reduces the number of bearings. In thisembodiment, a gear ratio ρ2 (number of teeth of the sun gear 65/numberof teeth of the ring gear 66) of the second change speed planetary gearmechanism PG2 is set slightly greater than a gear ratio ρ1 (number ofteeth of the sun gear 61/number of teeth of the ring gear 62) of thefirst change speed planetary gear mechanism PG1 (see FIG. 3). The gearratios ρ1 and ρ2 of the first and the second change speed planetary gearmechanisms PG1 and PG2 may be set to arbitrary values.

The hybrid electronic control unit 70 is constructed as a microprocessorincluding a CPU 72, a ROM 74 that stores processing programs, a RAM 76that temporarily stores data, and a non-illustrated input-output port,and a non-illustrated communication port. The hybrid electronic controlunit 70 receives various inputs via the input port: an ignition signalfrom an ignition switch (start switch) 80, a gearshift position SP froma gearshift position sensor 82 that detects the current position of agearshift lever 81, an accelerator opening Acc from an accelerator pedalposition sensor 84 that measures a step-on amount of an acceleratorpedal 83, a brake pedal position BP from a brake pedal position sensor86 that measures a step-on amount of a brake pedal 85, and a vehiclespeed V from a vehicle speed sensor 87. The hybrid electronic controlunit 70 communicates with the engine ECU 24, the motor ECU 30, and thebattery ECU 36 via the communication port to transmit diverse controlsignals and data to and from the engine ECU 24, the motor ECU 30, andthe battery ECU 36, as mentioned previously. The hybrid electroniccontrol unit 70 also controls clutch C0 and actuator 90-92 of brakeclutches BC1 and BC2 of transmission 60.

The operations of the hybrid vehicle 20 are described below withreference to FIGS. 3 through 12. During a drive of the hybrid vehicle 20in respective change speed states of FIGS. 3 to 8, under comprehensivecontrol of the hybrid ECU 70 based on the driver's depression amount ofan accelerator pedal 83 and the vehicle speed V, the engine 22 iscontrolled by the engine ECU 24, the motors MG1 and MG2 are controlledby the motor ECU 30, and the actuators 90 to 92 (the clutch C0 and thebrake clutches BC1 and BC2 of the transmission 60) are directlycontrolled by the hybrid ECU 70. In the drawings of FIGS. 3 through 8,an S-axis represents a rotation speed of the sun gear 41 in the powerdistribution integration mechanism 40 (equivalent to a rotation speedNm1 of the motor MG1 or the first motor shaft 46). An R-axis representsa rotation speed of the ring gear 42 in the power distributionintegration mechanism 40 (equivalent to a rotation speed Ne of theengine 22). A C-axis represents a rotation speed of the carrier 45 inthe power distribution integration mechanism 40 (equivalent to arotation speed of the carrier shaft 45 a). A 61-axis represents arotation speed of the sun gear 61 in the first change speed planetarygear mechanism PG1 of the transmission 60. A 66-axis represents arotation speed of the ring gear 66 in the second change speed planetarygear mechanism PG2. A 64-axis represents a rotation speed of the carrier64 in the transmission 60 (equivalent to a rotation speed of thedriveshaft 69). A 62-axis represents a rotation speed of the ring gear62 in the first change speed planetary gear mechanism PG1. A 65-axisrepresents a rotation speed of the sun gear 65 in the second changespeed planetary gear mechanism PG2.

During a drive of the hybrid vehicle 20 with engagement of the clutch C0and operation of the engine 22, the clutch position of the brake clutchBC1 is set to the R position to fix the ring gear 62 of the first changespeed planetary gear mechanism PG1 to the transmission case in thenon-rotatable manner, while the clutch position of the brake clutch BC2is set to the M position to decouple the power distribution integrationmechanism 40 (more specifically the sun gear 41) from the second changespeed planetary gear mechanism PG2 (more specifically the ring gear 66).Such settings of the clutch positions set the transmission 60 in a firstchange speed state (first speed) shown in FIG. 3. In this first changespeed state, the power of the carrier shaft 45 a (the carrier 45) issubjected to speed change at a change gear ratio (=ρ1/(1+ρ1)) based onthe gear ratio ρ1 of the first change speed planetary gear mechanism PG1and is transmitted to the driveshaft 69. In the first change speed stateof FIG. 3, on condition that the rotation speed Nm1 of the motor MG1(equivalent to the rotation speed of the sun gear 41 and the rotationspeed of the first motor shaft 46) is sufficiently close to the rotationspeed of the ring gear 66 in the second change speed planetary gearmechanism PG2, while the clutch position of the brake clutch BC1 is keptat the R position to fix the ring gear 62 in the first change speedplanetary gear mechanism PG1 in the non-rotatable manner, the clutchposition of the brake clutch BC2 may be changed to the R position tocouple the power distribution integration mechanism 40 (morespecifically the sun gear 41) with the second change speed planetarygear mechanism PG2 (more specifically the ring gear 66) as shown in FIG.4. In the description below, a mode of fixing the ring gear 62 of thefirst change speed planetary gear mechanism PG1 in the non-rotatablemanner by means of the brake clutch BC1 and coupling the powerdistribution integration mechanism 40 (the sun gear 41) with the secondchange speed planetary gear mechanism PG2 (the ring gear 46) by means ofthe brake clutch BC2 is referred to as ‘simultaneous engagement mode’.The state of FIG. 4 is specifically called ‘1^(st) speed-2^(nd) speedsimultaneous engagement state’. Setting torque commands of the motorsMG1 and MG2 to 0 in this 1^(st) speed-2^(nd) speed simultaneousengagement state causes the motors MG1 and MG2 to run idle withoutperforming either power operation or regenerative operation. The outputpower (torque) of the engine 22 is thus mechanically (directly)transmitted at a first fixed change gear ratio γ1(=(1−ρ)·ρ1/(1+ρ1)+ρ/(1+ρ2)) to the driveshaft 69 without conversion intoelectrical energy. In the 1^(st) speed-2^(nd) speed simultaneousengagement state of FIG. 4, while the clutch position of the brakeclutch BC2 is kept at the R position to keep the sun gear 41 of thepower distribution integration mechanism 40 coupled with the ring gear66 of the second change speed planetary gear mechanism PG2, the clutchposition of the brake clutch BC1 may be changed to the M position torelease the ring gear 62 of the first change speed planetary gearmechanism PG1 in the rotatable manner. Such settings of the clutchpositions set the transmission 60 in a second change speed state (secondspeed) allowing only transmission of the power by the second changespeed planetary gear mechanism PG2 as shown in FIG. 5. In this secondchange speed state, the power of the first motor shaft 46 (the sun gear41) is subjected to speed change at a change gear ratio (=1/(1+ρ2))based on the gear ratio p2 of the second change speed planetary gearmechanism PG2 and is transmitted to the driveshaft 69.

In the second change speed state of FIG. 5, on condition that therotation speeds of the sun gear 61, the ring gear 62, and the carrier 64of the first change speed planetary gear mechanism PG1 are almost equalto one another to allow substantially integral rotations of theseelements 61, 62, and 64, the clutch position of the brake clutch BC1 maybe changed to the L position to couple the ring gear 62 of the firstchange speed planetary gear mechanism PG1 with the carrier 64 as shownin FIG. 6. In the description below, a mode of coupling the ring gear 62of the first change speed planetary gear mechanism PG1 with the carrier64 by means of the brake clutch BC1 while keeping the power distributionintegration mechanism 40 (the sun gear 41) coupled with the secondchange speed planetary gear mechanism PG2 (the ring gear 66) by means ofthe brake clutch BC2 is also referred to as the ‘simultaneous engagementmode’. The state of FIG. 6 is specifically called ‘2^(nd) speed-3^(rd)speed simultaneous engagement state’. Setting torque commands of themotors MG1 and MG2 to 0 in this 2^(nd) speed-3^(rd) speed simultaneousengagement state causes the motors MG1 and MG2 to run idle withoutperforming either power operation or regenerative operation. The outputpower (torque) of the engine 22 is thus mechanically (directly)transmitted at a second fixed change gear ratio γ2 (=1−ρ+ρ/(1+ρ2)) tothe driveshaft 69 without conversion into electrical energy. In the2^(nd) speed-3^(rd) speed simultaneous engagement state of FIG. 6, theclutch position of the brake clutch BC2 may be changed to the M positionto release the ring gear 66 in the second change speed planetary gearmechanism PG2 in the rotatable manner. Such setting of the clutchposition sets the transmission 60 in a third change speed state (thirdspeed) as shown in FIG. 7. In this third change speed state, thefunction of the brake clutch BC1 substantially locks the sun gear 61,the ring gear 62, and the carrier 64 in the first change speed planetarygear mechanism PG1 to allow integral rotations of these elements 61, 62,and 64. The power of the carrier 45 in the power distributionintegration mechanism 40 is thus directly transmitted at a change gearratio of 1 to the driveshaft 69 via the carrier shaft 45 a and theintegrally rotating elements of the first change speed planetary gearmechanism PG1 as shown in FIG. 7. In the third change speed state, theratio of the rotation speed of the engine 22 to the rotation speed ofthe driveshaft 69 directly linked with the carrier 45 as the outputelement is varied continuously in a stepless manner by controlling therotation speed of the motor MG1.

In the third change speed state of FIG. 7, on condition that therotation speeds of the motor MG1, the first motor shaft 46, the sun gear41 of the power distribution integration mechanism 40, and the sun gear61 of the first change speed planetary gear mechanism PG1 approach to 0,the clutch position of the brake clutch BC2 may be changed to the Lposition to fix the sun gear 41 as the second element of the powerdistribution integration mechanism 40 in the non-rotatable manner viathe lock element 68 b, the engagement element 46 b, and the first motorshaft 46 as shown in FIG. 8. In the description below, a mode of fixingthe first motor shaft 46 (the motor MG1) in the non-rotatable manner bymeans of the brake clutch BC2 while keeping the ring gear 62 coupledwith the carrier 64 by means of the brake clutch BC1 to substantiallylock the first change speed planetary gear mechanism PG1 in thetransmission 60 is also referred to as the ‘simultaneous engagementmode’. The state of FIG. 8 is specifically called 3^(rd) speed OD(overdrive) state. Setting the torque commands of the motors MG1 and MG2to 0 in this 3^(rd) speed OD state causes the motors MG1 and MG2 to runidle without performing either power operation or regenerativeoperation. The output power (torque) of the engine 22 is thus directlytransmitted to the driveshaft 69 with speed change (speed increase) at athird fixed change gear ratio γ3 (=1/(1−ρ)) of less than 1 withoutconversion into electrical energy. The change gear ratio of thetransmission 60 may be shifted down according to the procedure reverseto the above description.

During the drive of the hybrid vehicle 20 with operation of the engine22, at the setting of the speed in the transmission 60 to either thefirst change speed state or the third change speed state, the motors MG1and MG2 may be driven and controlled to make the motor MG2, whichconnects with the carrier 45 of the power distribution integrationmechanism 40 working as the output element, function as the motor and tomake the motor MG1, which connects with the sun gear 41 working as thereactive element, function as the generator. In this state, the powerdistribution integration mechanism 40 distributes the power of theengine 22 input via the ring gear 42 at its gear ratio ρ into the sungear 41 and the carrier 45, while integrating the power of the engine 22with the power of the motor MG2 functioning as the motor and outputtingthe integrated power to the carrier 45. In the description below, a modeof making the motor MG1 function as the generator and making the motorMG2 function as the motor is referred to as ‘first torque conversionmode’. In the first torque conversion mode, the power of the engine 22goes through torque conversion by means of the power distributionintegration mechanism 40 and the motors MG1 and MG2 and is then outputto the carrier 45. The ratio of the rotation speed Ne of the engine 22to the rotation speed of the carrier 45 as the output element is variedcontinuously in a stepless manner by controlling the rotation speed ofthe motor MG1. FIG. 9 is an alignment chart showing torque-rotationspeed dynamics of the respective elements in the power distributionintegration mechanism 40 in the first torque conversion mode. TheS-axis, the R-axis, and the C-axis in FIG. 9 represent the same meaningsas those in FIGS. 3 through 8. In the alignment chart of FIG. 9, ρdenotes the gear ratio of the power distribution integration mechanism40 (number of teeth of the sun gear 41/number of teeth of the ring gear42). In FIG. 9, values above a O-axis (horizontal axis) and values belowthe O-axis respectively show positive rotation speeds and negativerotation speeds on the S-axis, the R-axis, and the C-axis. Thick arrowson the axes represent torques applied to the corresponding elements;upward arrows show application of positive torques and downward arrowsshow application of negative torques. These definitions are similarlyapplied to the alignment charts of FIGS. 3 through 8 explained above andthe alignment charts of FIGS. 10 and 11 explained later.

During the drive of the hybrid vehicle 20 with operation of the engine22, at the setting of the speed in the transmission 60 to the secondchange speed state, the motors MG1 and MG2 may be driven and controlledto make the motor MG1, which connects with the sun gear 41 of the powerdistribution integration mechanism 40 working as the output element,function as the motor and to make the motor MG2, which connects with thecarrier 45 working as the reactive element, function as the generator.In this state, the power distribution integration mechanism 40distributes the power of the engine 22 input via the ring gear 42 at itsgear ratio ρ into the sun gear 41 and the carrier 45, while integratingthe power of the engine 22 with the power of the motor MG1 functioningas the motor and outputting the integrated power to the sun gear 41. Inthe description below, a mode of making the motor MG2 function as thegenerator and making the motor MG1 function as the motor is referred toas ‘second torque conversion mode’. In the second torque conversionmode, the power of the engine 22 goes through torque conversion by meansof the power distribution integration mechanism 40 and the motors MG1and MG2 and is then output to the sun gear 41. The ratio of the rotationspeed Ne of the engine 22 to the rotation speed of the sun gear 41 asthe output element is varied continuously in a stepless manner bycontrolling the rotation speed of the motor MG2. FIG. 10 is an alignmentchart showing torque-rotation speed dynamics of the respective elementsin the power distribution integration mechanism 40 in the second torqueconversion mode.

In the hybrid vehicle 20 of the embodiment, the first torque conversionmode and the second torque conversion mode are alternately switched overwith a change of the change speed state (change gear ratio) in thetransmission 60. Such switchover prevents the rotation speed Nm1 or Nm2of the motor MG1 or MG2 functioning as the generator from having anegative value with an increase in rotation speed Nm2 or Nm1 of themotor MG2 or MG1 functioning as the motor. This arrangement of thehybrid vehicle 20 effectively prevents the occurrence of powercirculation in the first torque conversion mode, as well as theoccurrence of power circulation in the second torque conversion mode.The power circulation in the first torque conversion mode is triggeredby the negative rotation speed of the motor MG1 and causes the motor MG2to consume part of the power output to the carrier shaft 45 a andgenerate electric power, while causing the motor MG1 to consume theelectric power generated by the motor MG2 and output driving power. Thepower circulation in the second torque conversion mode is triggered bythe negative rotation speed of the motor MG2 and causes the motor MG1 toconsume part of the power output to the first motor shaft 46 andgenerate electric power, while causing the motor MG2 to consume theelectric power generated by the motor MG1 and output driving power. Suchprevention of the power circulation desirably improves the powertransmission efficiency in a wider drive range. The prevention of thepower circulation also reduces the maximum required rotation speeds ofthe motors MG1 and MG2 and thereby enables size reduction of the motorsMG1 and MG2. In the hybrid vehicle 20 of the embodiment, the outputpower of the engine 22 is mechanically (directly) transmittable to thedriveshaft 69 at the first through the third fixed change gear ratios γ1through γ3 uniquely set for the 1^(st) speed-2^(nd) speed simultaneousengagement state, the 2^(nd) speed-3^(rd) speed simultaneous engagementstate, and the 3^(rd) speed OD state. This arrangement desirablyincreases the potential for mechanical output of the power from theengine 22 to the driveshaft 69 without conversion into electrical energyand thereby further enhances the power transmission efficiency in thewider drive range. In a general power output apparatus equipped with anengine, two motors, and a differential rotation mechanism such as aplanetary gear mechanism, the relatively large reduction gear ratiobetween the engine and a driveshaft increases the potential forconversion of the engine output power into electrical energy. Thisundesirably decreases the power transmission efficiency and tends tocause heat generation in the motors MG1 and MG2. The simultaneousengagement mode described above is thus especially advantageous for therelatively large reduction gear ratio between the engine 22 and thedriveshaft 69.

The hybrid vehicle 20 may be driven in a motor drive mode, where atleast one of the motors MG1 and MG2 is driven with supply of electricpower from the battery 35 to output driving power, while the engine 22is at a stop as shown in FIG. 11. In the hybrid vehicle 20 of theembodiment, the motor drive mode includes three primary modes, aclutch-engaged one-motor drive mode, a clutch-released one-motor drivemode, and a two-motor drive mode. In the clutch-engaged one-motor drivemode, in the engaged position of the clutch C0, the transmission 60 isset to the first change speed state or the third change speed state toallow the power output from only the motor MG2 or is set to the secondchange speed state to allow the power output from only the motor MG1. Inthe clutch-engaged one-motor drive mode, the clutch C0 is set to connectthe sun gear 41 of the power distribution integration mechanism 40 withthe first motor shaft 46. The motor MG1 or MG2 in the state of no poweroutput thus follows the motor MG2 or MG1 in the state of power output torun idle as shown by the broken line in FIG. 11. In the clutch-releasedone-motor drive mode, in the released position of the clutch C0, thetransmission 60 is set to one of the first change speed state, the thirdchange speed state, and the 3^(rd) speed OD state to allow the poweroutput from only the motor MG2 or is set to the second change speedstate to allow the power output from only the motor MG1. In theclutch-released one-motor drive mode, the clutch C0 is released todisconnect the sun gear 41 from the first motor shaft 46. As shown bythe one-dot chain line and the two-dot chain line in FIG. 11, suchdisconnection effectively avoids the follow of the crankshaft 26 of theengine 22 at the stop, as well as the follow of the motor MG1 or MG2 inthe state of no power output, thus preventing a decrease in powertransmission efficiency. In the two-motor drive mode, in the releasedposition of the clutch C0, at least one of the motors MG1 and MG2 isdriven and controlled after the transmission 60 is set in either of the1^(st) speed-2^(nd) speed simultaneous engagement state and the 2^(nd)speed-3^(rd) speed simultaneous engagement state by means of the brakeclutches BC1 and BC2. Such setting and drive control effectively avoidsthe follow of the engine 22 and enables the power output from both themotors MG1 and MG2 and transmission of a large driving power to thedriveshaft 69 in the motor drive mode. This two-motor drive mode isespecially suitable for a hill start and ensures the favorable towingperformance during the motor drive of the hybrid vehicle 20.

In the hybrid vehicle 20 of the embodiment, in the clutch-releasedone-motor drive mode, the change speed state (change gear ratio) of thetransmission 60 is readily changeable to enable the efficient powertransmission to the driveshaft 69. For example, in the released positionof the clutch C0, the transmission 60 may be set in the first changespeed state to allow the power output from only the motor MG2 throughfixation of the ring gear 62 of the first change speed planetary gearmechanism PG1 to the transmission case by means of the brake clutch BC1.In order to shift up the change gear ratio of the transmission 60 fromthis state, the rotation speed Nm1 of the motor MG1 is synchronized withthe rotation speed of the ring gear 66 in the second change speedplanetary gear mechanism PG2. The brake clutch BC2 is then set to couplethe ring gear 66 of the second change speed planetary gear mechanism PG2with the sun gear 41 as the second element of the power distributionintegration mechanism 40. This shifts the transmission 60 from the firstchange speed state to the 1^(st) speed-2^(nd) speed simultaneousengagement state. The clutch position of the brake clutch BC1 issubsequently changed to the M position to release the ring gear 62 ofthe first change speed planetary gear mechanism PG1 in the rotatablemanner and to allow the power output from only the motor MG1. Thisshifts up the change gear ratio of the transmission 60 and sets thetransmission 60 in the second change speed state (second speed). In thereleased position of the clutch C0, the transmission 60 may be set inthe second change speed state to allow the power output from only themotor MG1. In order to shift up the change gear ratio of thetransmission 60 from this state, the motor MG2 is driven and controlledto synchronize the rotation speed of the ring gear 62 in the firstchange speed planetary gear mechanism PG1 with the rotation speed of thecarrier 64 (the driveshaft 69). The brake clutch BC1 is then set tocouple the ring gear 62 of the first change speed planetary gearmechanism PG1 with the carrier 64. This shifts the transmission 60 fromthe second change speed state to the 2^(nd) speed-3^(rd) speedsimultaneous engagement state. The clutch position of the brake clutchBC2 is subsequently changed to the M position to release the ring gear66 of the second change speed planetary gear mechanism PG2 in therotatable manner and to allow the power output from only the motor MG2.This shifts up the change gear ratio of the transmission 60 and sets thetransmission 60 in the third change speed state (third speed). Anupshift of the change gear ratio from the third change speed state tothe 3^(rd) speed OD state is similarly performed in the clutch-releasedone-motor drive mode. In the hybrid vehicle 20 of the embodiment, thetransmission 60 is used to change the rotation speed of the carriershaft 45 a and the first motor shaft 46 and amplify the torque in themotor drive mode. This arrangement desirably reduces the maximumrequired torques of the motors MG1 and MG2 and thereby enables sizereduction of the motors MG1 and MG2. In response to a shift change ofthe change gear ratio of the transmission 60 during the motor drive ofthe hybrid vehicle 20, the transmission 60 undergoes the simultaneousengagement mode or the two-motor drive mode. This arrangementeffectively prevents a torque loss on the occasion of a shift change ofthe change gear ratio and ensures an extremely smooth shift change ofthe change gear ratio with causing no significant shock.

The change gear ratio of the transmission 60 may be shifted down in themotor drive mode according to the procedure basically reverse to theabove description. In response to an increase in driving force demand orin response to a decrease in state of charge SOC of the battery 35 inthe clutch-engaged one-motor drive mode, the motor MG1 or MG2 to be madeinto the state of no power output corresponding to the setting of thechange gear ratio in the transmission 60 is driven and controlled tocrank and start up the engine 22. In response to an increase in drivingforce demand or in response to a decrease in state of charge SOC of thebattery 35 in the clutch-released one-motor drive mode, on the otherhand, the motor MG1 or MG2 in the state of no power output is driven andcontrolled to synchronize its rotation speed Nm1 or Nm2 with therotation speed of the sun gear 41 or with the rotation speed of thecarrier 45 in the power distribution integration mechanism 40. After theclutch C0 is engaged, the motor MG1 or MG2 is subsequently driven andcontrolled to motor and start up the engine 22. The engine 22 can thusbe started up with smooth power transmission to the driveshaft 69. At astartup of the engine 22 in the two-motor drive mode, after selection ofone of the motors MG1 and MG2 as a motor of continuously outputtingpower corresponding to a target change gear ratio set in thetransmission 60, power conversion is performed to transmit the power ofthe other motor MG2 or MG1 of not continuously outputting power to theone motor MG1 or MG2 of continuously outputting power. On completion ofthe power conversion, the clutch position of either the brake clutch BC2or the brake clutch BC1 is changed to the M position to disconnect theother motor MG2 or MG1 of not continuously outputting power from thetransmission 60. The other motor MG2 or MG1 is then driven andcontrolled to synchronize its rotation speed Nm2 or Nm1 with therotation speed of the carrier 45 or with the rotation speed of the sungear 41 in the power distribution integration mechanism 40. After theclutch C0 is engaged, the other motor MG2 or MG1 is driven andcontrolled to motor and start up the engine 22. The engine 22 can thusbe started up with smooth power transmission to the driveshaft 69. FIG.12 shows the settings of the clutch positions of the brake clutches BC1and BC2 and the clutch C0 during the drive of the hybrid vehicle 20.

As described above, the hybrid vehicle 20 of the embodiment is equippedwith the power distribution integration mechanism 40 constructed as thethree element-type planetary gear mechanism having a gear ratio ofapproximately 0.5. The power distribution integration mechanism 40 ofthis structure is small-sized and enables the motors MG1 and MG2 to haveidentical specifications without requiring a reduction gear mechanism orany equivalent mechanism. This arrangement thus contributes to sizereduction of the power output apparatus including the engine 22, themotors MG1 and MG2, the power distribution integration mechanism 40, andthe transmission 60. The hybrid vehicle 20 of the embodiment is alsoequipped with the transmission 60 including the three element-type firstchange speed planetary gear mechanism PG1 and the three element-typesecond change speed planetary gear mechanism PG2. The transmission 60 isarranged coaxially with and in the downstream of the engine 22, themotors MG1 and MG2, and the power distribution integration mechanism 40.The structure of the transmission 60 enables size reduction both in theaxial direction and in the radial direction, compared with the parallelshaft-type transmission. The combination of the power distributionintegration mechanism 40 constructed as the three element-type planetarygear mechanism having the gear ratio of approximately 0.5 with thetransmission 60 including the three element-type first change speedplanetary gear mechanism PG1 and the three element-type second changespeed planetary gear mechanism PG2 desirably downsizes the power outputapparatus to be extremely favorable for mounting on the hybrid vehicle20 having a rear wheel drive system as a main drive system with the reardrive wheels RWa and RWb. The power distribution integration mechanism40 is constructed as the double pinion planetary gear mechanismincluding the ring gear 42 (third element), the sun gear 41 (secondelement), and the carrier 45 (first element) arranged to supportmultiple sets of the two intermeshing pinion gears 43 and 44 engagingwith the ring gear 42 and with the sun gear 41 and is arranged to havethe gear ratio ρ of approximately 0.5. This arrangement desirablyreduces the outer diameter of the power distribution integrationmechanism 40 and enables further size reduction of the whole poweroutput apparatus.

In the structure of the transmission 60 of the embodiment, the brakeclutch BC1 (first fixation structure) is set to fix the ring gear 62 asthe fixable element of the first change speed planetary gear mechanismPG1 in the non-rotatable manner, while the brake clutch BC2(transmission state changeover structure or the coupling-decouplingstructure) is set to decouple the power distribution integrationmechanism 40 (the sun gear 41) from the second change speed planetarygear mechanism PG2 (the ring gear 66) and disable the power transmissionvia the second change speed planetary gear mechanism PG2. In this firstchange speed state, such setting causes the carrier 45 of the powerdistribution integration mechanism 40 to work as the output element andenables the motor MG2 connecting with the carrier 45 to function as themotor, while enabling the motor MG1 connecting with the sun gear 41working as the reactive element to function as the generator. The brakeclutch BC1 is set to couple the ring gear 62 of the first change speedplanetary gear mechanism PG1 with the carrier 64, while the brake clutchBC2 is set to release the ring gear 66 of the second change speedplanetary gear mechanism PG2 in the rotatable manner. In this thirdchange speed state, such setting causes the carrier 45 of the powerdistribution integration mechanism 40 to work as the output element andenables the motor MG2 connecting with the carrier 45 to function as themotor, while enabling the motor MG1 connecting with the sun gear 41working as the reactive element to function as the generator. In thetransmission 60 of the embodiment, the brake clutch BC1 is set torelease the ring gear 62 of the first change speed planetary gearmechanism PG1 in the rotatable manner and disable the power transmissionvia the first change speed planetary gear mechanism PG1, while the brakeclutch BC2 is set to couple the sun gear 41 of the power distributionintegration mechanism 40 with the ring gear 66 of the second changespeed planetary gear mechanism PG2 and enable the power transmission viathe second change speed planetary gear mechanism PG2. In this secondchange speed state, such setting causes the sun gear 41 of the powerdistribution integration mechanism 40 to work as the output element andenables the motor MG1 connecting with the sun gear 41 to function as themotor, while enabling the motor MG2 connecting with the carrier 45working as the reactive element to function as the generator. In thehybrid vehicle 20 of the embodiment, the clutch positions of the brakeclutches BC1 and BC2 are adequately controlled to change the changespeed state of the transmission 60. This arrangement effectivelyprevents the occurrence of power circulation that is triggered by thenegative rotation speed of the motor MG1 or MG2 functioning as thegenerator in response to an increase in rotation speed of the motor MG2or MG1 functioning as the motor.

In the structure of the transmission 60 of the embodiment, the brakeclutch BC1 is set to fix the ring gear 62 of the first change speedplanetary gear mechanism PG1 in the non-rotatable manner, while thebrake clutch BC2 is set to couple the sun gear 41 of the powerdistribution integration mechanism 40 with the ring gear 66 of thesecond change speed planetary gear mechanism PG2 and enable the powertransmission via the second change speed planetary gear mechanism PG2.In this 1^(st) speed-2^(nd) speed simultaneous engagement state, suchsetting enables the power of the engine 22 to be mechanically (directly)transmitted to the driveshaft 69 at the first fixed change gear ratioγ1. The brake clutch BC1 (coupling structure) is set to couple the ringgear 62 (fixable element) of the first change speed planetary gearmechanism PG1 with the carrier 64 (output element), while the brakeclutch BC2 is set to couple the sun gear 41 of the power distributionintegration mechanism 40 with the ring gear 66 of the second changespeed planetary gear mechanism PG2 and enable the power transmission viathe second change speed planetary gear mechanism PG2. In this 2^(nd)speed-3^(rd) speed simultaneous engagement state, such setting enablesthe power of the engine 22 to be mechanically (directly) transmitted tothe driveshaft 69 at the second fixed change gear ratio γ2, which isdifferent from the first fixed change gear ratio γ1 in the 1^(st)speed-2^(nd) speed simultaneous engagement state of fixing the ring gear62 of the first change speed planetary gear mechanism PG1 by means ofthe brake clutch BC1 and enabling the power transmission via the secondchange speed planetary gear mechanism PG2 by means of the brake clutchBC2. In the 2^(nd) speed-3^(rd) speed simultaneous engagement state,setting the brake clutch BC2 to release the ring gear 66 of the secondchange speed planetary gear mechanism PG2 in the rotatable manner anddisable the power transmission via the second change speed planetarygear mechanism PG2 causes the brake clutch BC1 to substantially lock andintegrally rotate the sun gear 61, the ring gear 62, and the carrier 64of the first change speed planetary gear mechanism PG1. In this thirdchange speed state, such setting enables direct transmission of thepower from the carrier 45 of the power distribution integrationmechanism 40 to the driveshaft 69 at the change gear ratio of 1. In thethird change speed state of coupling the ring gear 62 of the firstchange speed planetary gear mechanism PG1 with the carrier 64, the brakeclutch BC2 (third fixation structure) is set to fix the sun gear 41(reactive element) of the power distribution integration mechanism 40connecting with the motor MG1 functioning as the generator in thenon-rotatable manner. In this 3^(rd) speed OD state, such settingenables the power of the engine 22 to be subjected to the speed increaseat the third fixed change gear ratio γ3 of less than 1 and to bedirectly transmitted to the driveshaft 69. The hybrid vehicle 20 of theembodiment accordingly has the improved power transmission efficiency ina wider drive range, thus ensuring the enhanced fuel efficiency and theimproved driving performance.

The transmission 60 includes the single pinion first change speedplanetary gear mechanism PG1 and the single pinion second change speedplanetary gear mechanism PG2. The first change speed planetary gearmechanism PG1 has the sun gear 61 as the input element, the ring gear 62as the fixable element, and the carrier 64 as the output element tosupport the multiple pinion gears 63 engaging with both the sun gear 61and the ring gear 62. The second change speed planetary gear mechanismPG2 has the ring gear 66 as the input element, the sun gear 65 as thefixable element, and the common carrier 64 shared with the first changespeed planetary gear mechanism PG1 and arranged to hold the multiplepinion gears 67 engaging with both the ring gear 66 and the sun gear 65.The construction of such single pinion planetary gear mechanisms as thefirst and the second change speed planetary gear mechanisms PG1 and PG2desirably downsizes the transmission 60 and thereby the whole poweroutput apparatus. In the structure of the embodiment, the sun gear 65 ofthe second change speed planetary gear mechanism PG2 is attached to thehollow sun gear shaft 65 a. The ring gear 66 of the second change speedplanetary gear mechanism PG2 is connectable with the sun gear 41 of thepower distribution integration mechanism 40 (the first motor shaft 46)via the ring gear shaft 66 a located in and passed through the hollowsun gear shaft 65 a. This arrangement makes space for the support member65 y between the second change speed planetary gear mechanism PG2 andthe brake clutch BC2 settable to couple the sun gear 41 of the powerdistribution integration mechanism 40 (the first motor shaft 46) withthe ring gear shaft 66 a (the ring gear 66) as shown in FIG. 2. Thislayout allows the ring gear 66 as the input element of the second changespeed planetary gear mechanism PG2 to be coupled with the sun gear 41 ofthe power distribution integration mechanism 40, while the sun gear 65as the fixable element of the second change speed planetary gearmechanism PG2 is fastened to the transmission case in the non-rotatablemanner. The single brake clutch BC1 is used both as the first fixationstructure to fix and release the ring gear 62 of the first change speedplanetary gear mechanism PG1 and as the coupling structure to couple anddecouple the ring gear 62 with and from the carrier 64. This arrangementdesirably downsizes the transmission 60 and the whole power outputapparatus, while simplifying the structure of the transmission 60 andthe whole power output apparatus. Similarly the single brake clutch BC2is used both as the coupling-decoupling structure to couple and decouplethe sun gear 41 of the power distribution integration mechanism 40 withand from the ring gear 66 of the second change speed planetary gearmechanism PG2 and as the third fixation structure to fix the sun gear 41of the power distribution integration mechanism 40 in the non-rotatablemanner. This arrangement desirably downsizes the transmission 60 and thewhole power output apparatus, while simplifying the structure of thetransmission 60 and the whole power output apparatus. The functions ofthe brake clutches BC1 and BC2 may be separated into clutches havingclutch functions and brakes having brake functions.

FIG. 13 shows the schematic structure of another transmission 60Aapplicable to the hybrid vehicle 20 of the embodiment described above.The transmission 60A of FIG. 13 includes single pinion-type first andsecond change speed planetary gear mechanisms PG1 and PG2 and brakeclutches BC1 and BC2 similar to those in the transmission 60. In thetransmission 60A, a sun gear 65 of the second change speed planetarygear mechanism PG2 is attached to a hollow sun gear shaft 65 a fastenedto the transmission case via a support member 65 y. A common carrier 64shared by the first and the second change speed planetary gearmechanisms PG1 and PG2 has a holder element 64 y to hold multiple piniongears 67 and a shaft element 64 x located in and passed through thehollow sun gear shaft 65 a. In the transmission 60A, the holder element64 y to hold the pinion gears 67 of the second change speed planetarygear mechanism PG2 is connected with the driveshaft 69 via the shaftelement 64 x located in and passed through the hollow sun gear shaft 65a. The holder element 64 y is provided at a position of not interferingwith the brake clutch BC2 settable to couple the sun gear 41 of thepower distribution integration mechanism 40 (the first motor shaft 46)with the ring gear shaft 66 a (the ring gear 66). This layout also makesspace for the support member 65 y between the second change speedplanetary gear mechanism PG2 and the first change speed planetary gearmechanism PG1. In the transmission 60A of FIG. 13, the ring gear 66 asthe input element of the second change speed planetary gear mechanismPG2 may be coupled with the sun gear 41 of the power distributionintegration mechanism 40, while the sun gear 65 as the fixable elementof the second change speed planetary gear mechanism PG2 is fastened tothe transmission case in a non-rotatable manner.

FIG. 14 shows the schematic structure of still another transmission 60Bapplicable to the hybrid vehicle 20 of the embodiment described above.The transmission 60B of FIG. 14 includes a brake clutch BC2′ and a brakeB3, in addition to single pinion-type first and second change speedplanetary gear mechanisms PG1 and PG2 and a brake clutch BC1 similar tothose in the transmission 60. In the transmission 60B, a ring gear 66 asthe input element of the second change speed planetary gear mechanismPG2 is attached to a mounting element 46 y at a position rearward of thesun gear 65 and the pinion gears 67 but forward of the first changespeed planetary gear mechanism PG1 in the vehicle body. The mountingelement 46 y is provided at one end of a first motor shaft 46 protrudedfrom a hollow sun gear shaft 65 a extended from a sun gear 65. A carrier64 is formed to be extended from outside of the ring gear 66 and goaround to the forward of the pinion gears 67. An engagement element 64 bis formed on the circumference of the carrier 64 at a position forwardof an engagement element 64 a in the vehicle body. The brake B3 isconstructed as a dog clutch including a movable engaging member EM3 andan electromagnetic, electric, or hydraulic actuator (not shown) to movethe movable engagement member EM3 back and forth in the axial directionof the first motor shaft 46. The movable engaging member EM3 is designedto continuously engage with a mating engagement element 46 c provided onone end of the first motor shaft 46 (right end in the drawing) and to beengageable with a lock element 68 c fixed to the transmission case.Namely the brake B3 performs part of the functions of the brake clutchBC2 included in the transmission 60 described above to fix the sun gear41 of the power distribution integration mechanism 40 to thetransmission case in the non-rotatable manner. The brake B3 functioningas the third fixation structure may be designed to fix the carrier 45 asthe first element of the power distribution integration mechanism 40 inthe non-rotatable manner and may be separately provided from thetransmission 60B.

The brake clutch BC2′ is constructed as a dog clutch including a movableengaging member EM2 and an electromagnetic, electric, or hydraulicactuator (not shown) to move the movable engagement member EM2 back andforth in the axial direction of the first motor shaft 46. The movableengaging member EM2 is designed to continuously engage with a matingengagement element 65 b provided on the sun gear shaft 65 a extendedfrom the sun gear 65 of the second change speed planetary gear mechanismPG2 and to be engageable both with a lock element 68 b fixed to thetransmission case and with the engagement element 64 b provided on thecircumference of the carrier 64. As shown in FIG. 14, the brake clutchBC2′ is structured to selectively change over the clutch position or theposition of the movable engaging member EM2 between multiple options ‘Rposition’, ‘M position’, and ‘L position’. At the setting of the clutchposition of the brake clutch BC2′ to the L position, the movableengaging member EM2 engages with both the engagement element 65 b of thesun gear shaft 65 a and the lock element 68 b fixed to the transmissioncase. Such setting causes the sun gear 65 as the fixable element of thesecond change speed planetary gear mechanism PG2 to be fastened to thetransmission case in the non-rotatable manner and thereby enables thepower transmission via the second change speed planetary gear mechanismPG2. At the setting of the clutch position of the brake clutch BC2′ tothe M position, the movable engaging member EM2 engages with only theengagement element 65 b of the sun gear shaft 65 a. Such settingreleases the sun gear 65 of the second change speed planetary gearmechanism PG2 in the rotatable manner. While the brake clutch BC2enables or disables the power input into the second change speedplanetary gear mechanism PG2 (the ring gear 66), the brake clutch BC2′fixes the sun gear 65 as the fixable element of the second change speedplanetary gear mechanism PG2 in the non-rotatable manner to enable thepower transmission via the second change speed planetary gear mechanismPG2 or releases the sun gear 65 in the rotatable manner to disable thepower transmission via the second change speed planetary gear mechanismPG2. At the setting of the clutch position of the brake clutch BC2′ tothe R position, the movable engaging member EM2 engages with both theengagement element 65 b of the sun gear shaft 65 a and the engagementelement 64 b of the carrier 64. Such setting enables the sun gear 65 asthe fixable element to be coupled with the carrier 64 as the outputelement in the second change speed planetary gear mechanism PG2. FIG. 15shows the settings of the clutch positions of the brake clutches BC1 andBC2′, the brake B3, and the clutch C0 during the drive of the hybridvehicle 20 equipped with the transmission 60B including the brake clutchBC2′.

As described above, the transmission 60B of FIG. 14 includes the brakeclutch BC2′ (second fixation structure and second coupling structure)arranged to couple and decouple the sun gear 65 as the fixable elementof the second change speed planetary gear mechanism PG2 with and fromthe carrier 64, in addition to the brake clutch BC1 (first couplingstructure) arranged to couple and decouple the ring gear 62 as thefixable element of the first change speed planetary gear mechanism PG1with and from the carrier 64. In the transmission 60B of this modifiedexample, the brake clutch BC2′ is set to fix the sun gear 65 as thefixable element of the second change speed planetary gear mechanism PG2to the transmission case in the non-rotatable manner and thereby enablethe power transmission via the second change speed planetary gearmechanism PG2, while the brake clutch BC1 is set to couple the ring gear62 of the first change speed planetary gear mechanism PG1 with thecarrier 64. In this 2^(nd) speed-3^(rd) speed simultaneous engagementstate, such setting enables the power of the engine 22 to bemechanically (directly) transmitted to the driveshaft 69 at the secondfixed change gear ratio γ2, which is different from the first fixedchange gear ratio γ1 in the 1^(st) speed-2^(nd) speed simultaneousengagement state of fixing the ring gear 62 of the first change speedplanetary gear mechanism PG1 by means of the brake clutch BC1 andenabling the power transmission via the second change speed planetarygear mechanism PG2 by means of the brake clutch BC2′. In the 2^(nd)speed-3^(rd) speed simultaneous engagement state, setting the brakeclutch BC2′ to release the sun gear 65 of the second change speedplanetary gear mechanism PG2 in the rotatable manner and disable thepower transmission via the second change speed planetary gear mechanismPG2 causes the brake clutch BC1 to substantially lock and integrallyrotate the sun gear 61, the ring gear 62, and the carrier 64 of thefirst change speed planetary gear mechanism PG1. In this third changespeed state, such setting enables direct transmission of the power fromthe carrier 45 of the power distribution integration mechanism 40 to thedriveshaft 69 at the change gear ratio of 1. In the third change speedstate, on condition that the rotation speeds of the sun gear 41 (themotor MG1), the ring gear 42 (the engine 22), and the carrier 45 (themotor MG2) of the power distribution integration mechanism 40 are almostequal to one another, while the brake clutch BC1 keeps the ring gear 62as the fixable element of the first change speed planetary gearmechanism PG1 coupled with the carrier 64 as the output element, thebrake clutch BC2′ may couple the sun gear 65 as the fixable element ofthe second change speed planetary gear mechanism PG2 with the carrier 64as the output element as shown in FIG. 16. In the description below, amode of coupling the ring gear 62 of the first change speed planetarygear mechanism PG1 with the carrier 64 by means of the brake clutch BC1while coupling the sun gear 65 of the second change speed planetary gearmechanism PG2 with the carrier 64 by means of the brake clutch BC2′ isalso referred to as the ‘simultaneous engagement mode’. The state ofFIG. 16 is specifically called ‘equal rotation transmission state’. Inthis equal rotation transmission state, the sun gear 41, the ring gear42 (the engine 22), and the carrier 45 of the power distributionintegration mechanism 40, the sun gear 61 and the ring gear 62 of thefirst change speed planetary gear mechanism PG1, the sun gear 65 and thering gear 66 of the second change speed planetary gear mechanism PG2,and the common carrier 64 shared by the first and second change speedplanetary gear mechanisms PG1 and PG2 are integrally rotated as shown inFIG. 16. In the equal rotation transmission state, the output power ofthe engine 22 is thus mechanically (directly) transmitted at change gearratio of 1 to the driveshaft 69. Namely the transmission 60B enables theoutput power of the engine 22 to be mechanically (directly) transmittedto the driveshaft 69 at the change gear ratio of 1 in the equal rotationtransmission state of FIG. 16, which is different from the 1^(st)speed-2^(nd) speed simultaneous engagement state, the 2^(nd)speed-3^(rd) speed simultaneous engagement state, and the 3^(rd) speedOD state. The use of the transmission 60B thus ensures the enhancedpower transmission efficiency in a wider drive range. The transmission60B includes the single brake clutch BC2′ functioning both as the secondfixation structure to fix and release the sun gear 65 of the secondchange speed planetary gear mechanism PG2 and as the second couplingstructure to couple and decouple the sun gear 65 with and from thecarrier 64, in addition to the single brake clutch BC1 functioning bothas the first fixation structure to fix and release the ring gear 62 ofthe first change speed planetary gear mechanism PG1 and as the firstcoupling structure to couple and decouple the ring gear 62 with and fromthe carrier 64. This arrangement desirably downsizes the transmission60B and the whole power output apparatus, while simplifying thestructure of the transmission 60B and the whole power output apparatus.

FIG. 17 shows the schematic structure of another transmission 100applicable to the hybrid vehicle 20 of the embodiment described above.The transmission 100 shown in FIG. 17 includes a single pinion firstchange speed planetary gear mechanism 110, a second change speedplanetary gear mechanism 120, and brake clutches BC1 and BC2. The firstchange speed planetary gear mechanism 110 includes a sun gear 111 as aninput element, a ring gear 112 as a fixable element, and a carrier 114as an output element arranged to hold pinion gears 113 engaging with thesun gear 111 and with the ring gear 112. The second change speedplanetary gear mechanism 120 includes a first sun gear 121 as an inputelement, a second sun gear 122 as an output element arranged to have adifferent number of teeth from that of the first sun gear 121 and toconnect with the carrier 114 of the first change speed planetary gearmechanism 110 and with the driveshaft 69, and a carrier 126 as a fixableelement arranged to hold a stepped gear 125 of linking a first piniongear 123 engaging with the first sun gear 121 to a second pinion gear124 engaging with the second sun gear 122. In the transmission 100 ofFIG. 17, the carrier 126 of the second change speed planetary gearmechanism 120 is fastened to the transmission case. The single brakeclutch BC1 functions both as a fixation structure to fix and release thering gear 112 of the first change speed planetary gear mechanism 110 andas a coupling structure to couple and decouple the ring gear 112 withand from the carrier 114. The brake clutch BC2 includes a movableengaging member EM2 and an electromagnetic, electric, or hydraulicactuator (not shown) to move the movable engagement member EM2 back andforth in the axial direction of the first motor shaft 46. The movableengaging member EM2 is designed to continuously engage with a matingengagement element 46 b provided on one end of the first motor shaft 46and to be engageable both with an engagement element 121 b provided on asun gear shaft 121 a extended from the first sun gear 121 of the secondchange speed planetary gear mechanism 120 and with a lock element 68 bfixed to the transmission case. The brake clutch BC2 of the transmission100 couples the first sun gear 121 as the input element of the secondchange speed planetary gear mechanism 120 with the sun gear 41 as thesecond element of the power distribution integration mechanism 40 viathe sun gear shaft 121 a, the first motor shaft 46, and the clutch C0 toenable the power input into the second change speed planetary gearmechanism 120 (the first sun gear 121). The brake clutch BC2 alsodecouples the first sun gear 121 of the second change speed planetarygear mechanism 120 from the sun gear 41 as the second element of thepower distribution integration mechanism 40 to disable the power inputinto the second change speed planetary gear mechanism 120 (the first sungear 121). The combination of the single pinion first change speedplanetary gear mechanism 110 with the second change speed planetary gearmechanism 120 arranged to include the stepped gear 125 and accordinglyhave a smaller dimension in the radial direction than the single pinionplanetary gear mechanism desirably ensures size reduction of thetransmission 100 especially in the radial direction.

FIG. 18 shows the schematic structure of another transmission 100Aapplicable to the hybrid vehicle 20 of the embodiment described above.The transmission 100A shown in FIG. 18 includes a brake B3 and a brakeclutch BC2′, in addition to the first change speed planetary gearmechanism 110, the second change speed planetary gear mechanism 120, andthe brake clutch BC1 similar to those included in the transmission 100described above with reference to FIG. 17. In the transmission 100A, thecarrier 126 as the fixable element of the second change speed planetarygear mechanism 120 has a substantially cylindrical circumferential partwith an engagement element 126 b formed thereon to continuously engagewith a movable engaging element EM2 of the brake clutch BC2′. Themovable engaging element EM2 of the brake clutch BC2′ is arranged to beengageable both with an engagement element 114 b provided on the carrier114 of the first change speed planetary gear mechanism 110 and with alock element 68 b fastened to the transmission case. As shown in FIG.18, the brake clutch BC2′ is structured to selectively change over theclutch position or the position of the movable engaging member EM2between multiple options ‘R position’, ‘M position’, and ‘L position’.In the transmission 100A, at the setting of the clutch position of thebrake clutch BC2′ to the L position, the movable engaging member EM2engages with both the engagement element 126 b of the carrier 126 in thesecond change speed planetary gear mechanism 120 and the lock element 68b fixed to the transmission case. Such setting causes the carrier 126 asthe fixable element of the second change speed planetary gear mechanism120 to be fastened to the transmission case in the non-rotatable mannerand thereby enables the power transmission via the second change speedplanetary gear mechanism 120. At the setting of the clutch position ofthe brake clutch BC2′ to the M position, the movable engaging member EM2engages with only the engagement element 126 b of the carrier 126. Suchsetting releases the carrier 126 of the second change speed planetarygear mechanism 120 in the rotatable manner. Namely the brake clutch BC2′of the transmission 100A is configured to fix the carrier 126 as thefixable element of the second change speed planetary gear mechanism 120in the non-rotatable manner and thereby enable the power transmissionvia the second change speed planetary gear mechanism 120 and to releasethe carrier 126 in the rotatable manner and thereby disable the powertransmission via the second change speed planetary gear mechanism 120.At the setting of the clutch position of the brake clutch BC2′ to the Rposition, the movable engaging element EM2 engages with both theengagement element 126 b of the carrier 126 as the fixable element ofthe second change speed planetary gear mechanism 120 and the engagementelement 114 b of the carrier 114 in the first change speed planetarygear mechanism 110. Such setting couples the carrier 126 as the fixableelement with the second sun gear 122 as the output element in the secondchange speed planetary gear mechanism 120. As in the transmission 60Bdescribed above, setting the clutch position of the brake clutch BC1 tothe L position and the clutch position of the brake clutch BC2′ to the Rposition sets the transmission 100A in the equal rotation transmissionstate.

FIG. 19 shows the schematic structure of another transmission 200applicable to the hybrid vehicle 20 of the embodiment described above.The transmission 200 shown in FIG. 19 includes a single pinion firstchange speed planetary gear mechanism 210, a double pinion second changespeed planetary gear mechanism 220, and brake clutches BC1 and BC2. Thefirst change speed planetary gear mechanism 210 includes a sun gear 211as an input element, a ring gear 212 as a fixable element, and a carrier214 as an output element arranged to hold pinion gears 213 engaging withthe sun gear 211 and with the ring gear 212. The second change speedplanetary gear mechanism 220 includes a sun gear 221 as an inputelement, a ring gear 222 as an output element arranged to connect withthe carrier 214 of the first change speed planetary gear mechanism 210and with the driveshaft 69, and a carrier 225 as a fixable elementarranged to hold sets of two intermeshing pinion gears 223 and 224engaging with the sun gear 221 and with the ring gear 222. In thetransmission 200 shown in FIG. 19, the carrier 225 of the second changespeed planetary gear mechanism 220 is fastened to the transmission case.The single brake clutch BC1 functions both as a fixation structure tofix and release the ring gear 212 of the first change speed planetarygear mechanism 210 and as a coupling structure to couple and decouplethe ring gear 212 with and from the carrier 214. The brake clutch BC2includes a movable engaging member EM2 and an electromagnetic, electric,or hydraulic actuator (not shown) to move the movable engagement memberEM2 back and forth in the axial direction of the first motor shaft 46.The movable engaging member EM2 is designed to continuously engage witha mating engagement element 46 b provided on one end of the first motorshaft 46 and to be engageable both with an engagement element 221 bprovided on a sun gear shaft 221 a extended from the sun gear 221 of thesecond change speed planetary gear mechanism 220 and with a lock element68 b fixed to the transmission case. The brake clutch BC2 of thetransmission 200 couples the sun gear 221 as the input element of thesecond change speed planetary gear mechanism 220 with the sun gear 41 asthe second element of the power distribution integration mechanism 40via the sun gear shaft 221 a, the first motor shaft 46, and the clutchC0 to enable the power input into the second change speed planetary gearmechanism 220 (the sun gear 221). The brake clutch BC2 also decouplesthe sun gear 221 of the second change speed planetary gear mechanism 220from the sun gear 41 as the second element of the power distributionintegration mechanism 40 to disable the power input into the secondchange speed planetary gear mechanism 220 (the sun gear 221). Thetransmission 200 including the single pinion first change speedplanetary gear mechanism 210 in combination with the double pinionsecond change speed planetary gear mechanism 220 has the similarfunctions and effects to those of the transmission 60 in the embodimentand those of the transmission 100 in the modified example describedabove.

FIG. 20 shows the schematic structure of another transmission 200Aapplicable to the hybrid vehicle 20 of the embodiment described above.The transmission 200A shown in FIG. 20 includes a brake B3 and a brakeclutch BC2′, in addition to the single pinion first change speedplanetary gear mechanism 210, the double pinion second change speedplanetary gear mechanism 220, and the brake clutch BC1 similar to thoseincluded in the transmission 200 described above with reference to FIG.19. In the transmission 200A, the carrier 225 as the fixable element ofthe second change speed planetary gear mechanism 220 has an engagementelement 225 b provided to continuously engage with a movable engagingmember EM2 of the brake clutch BC2′. The movable engaging element EM2 ofthe brake clutch BC2′ is arranged to be engageable both with anengagement element 222 b provided on the ring gear 222 as the outputelement of the second change speed planetary gear mechanism 220 and witha lock element 68 b fastened to the transmission case. As shown in FIG.20, the brake clutch BC2′ is structured to selectively change over theclutch position or the position of the movable engaging member EM2between multiple options ‘R position’, ‘M position’, and ‘L position’.In the transmission 200A, at the setting of the clutch position of thebrake clutch BC2′ to the L position, the movable engaging member EM2engages with both the engagement element 225 b of the carrier 225 in thesecond change speed planetary gear mechanism 220 and the lock element 68b fixed to the transmission case. Such setting causes the carrier 225 asthe fixable element of the second change speed planetary gear mechanism220 to be fastened to the transmission case in the non-rotatable mannerand thereby enables the power transmission via the second change speedplanetary gear mechanism 220. At the setting of the clutch position ofthe brake clutch BC2′ to the M position, the movable engaging member EM2engages with only the engagement element 225 b of the carrier 225. Suchsetting releases the carrier 225 of the second change speed planetarygear mechanism 220 in the rotatable manner. Namely the brake clutch BC2′of the transmission 200A is configured to fix the carrier 225 as thefixable element of the second change speed planetary gear mechanism 220in the non-rotatable manner and thereby enable the power transmissionvia the second change speed planetary gear mechanism 220 and to releasethe carrier 225 in the rotatable manner and thereby disable the powertransmission via the second change speed planetary gear mechanism 220.At the setting of the clutch position of the brake clutch BC2′ to the Rposition, the movable engaging element EM2 engages with both theengagement element 225 b of the carrier 225 as the fixable element ofthe second change speed planetary gear mechanism 220 and the engagementelement 222 b of the ring gear 222 in the second change speed planetarygear mechanism 220. Such setting couples the carrier 225 as the fixableelement with the ring gear 222 as the output element in the secondchange speed planetary gear mechanism 220. As in the transmissions 60Band 100A described above, setting the clutch position of the brakeclutch BC1 to the L position and the clutch position of the brake clutchBC2′ to the R position sets the transmission 200A in the equal rotationtransmission state.

In the hybrid vehicle 20 of the embodiment, the clutch C0 is notrestricted to the element of coupling and decoupling the sun gear 41with and from the motor MG1. The clutch C0 may alternatively be arrangedto couple and decouple the carrier 45 (first element) with and from thecarrier shaft 45 a (motor MG2) or may otherwise be arranged to coupleand decouple the crankshaft 26 of the engine 22 with and from the ringgear 42 (third element). The hybrid vehicle 20 of the embodiment may beconstructed as a rear wheel drive-based four wheel drive vehicle. In theembodiment and its modified examples described above, the power outputapparatus is mounted on the hybrid vehicle 20. The power outputapparatus of the invention is, however, not restrictively mounted on thehybrid vehicle, but may be mounted on diversity of moving bodiesincluding various automobiles and other vehicles, boats and ships, andair craft or may be built in stationary equipment including constructionmachinery.

The primary elements in the embodiment and its modified examples aremapped to the primary constituents in the claims of the invention asdescribed below. The engine 22, the motor MG2 arranged to enable powerinput and power output, the motor MG1 arranged to enable power input andpower output, and the battery 35 arranged to enable transmission ofelectric power from and to the motors MG1 and MG2 in the embodiment andits modified examples are respectively equivalent to the ‘internalcombustion engine’, the ‘first motor’, the ‘second motor’, and the‘accumulator’ of the invention. The power distribution integrationmechanism 40 and the transmission 60, 60A, 60B, 100, 100A, 200, or 200Aare respectively equivalent to the ‘power distribution integrationmechanism’ and the ‘change speed transmission assembly’ of theinvention. The ‘internal combustion engine’ is not restricted to theengine 22 that receives a supply of a hydrocarbon fuel, such as gasolineor light oil, and outputs power, but may be an engine of any otherdesign, for example, a hydrogen engine. The ‘first motor’ and the‘second motor’ are not restricted to the motors MG1 and MG2 constructedas the synchronous motor generators but may be motors of any otherdesign, for example, induction motors. The ‘accumulator’ is notrestricted to the battery 35 constructed as the secondary cell but maybe any equivalent unit, for example, a capacitor, that enablestransmission of electric power to and from the first motor and thesecond motor. The ‘power distribution integration mechanism’ is notrestricted to the power distribution integration mechanism 40 but may beany planetary gear mechanism constructed to include a first elementconnecting with a rotating shaft of the first motor, a second elementconnecting with a rotating shaft of the second motor, and a thirdelement connecting with an engine shaft of the internal combustionengine, to allow mutually differential rotations of the three elements,and to have a gear ratio of approximately 0.5. For example, theplanetary gear mechanism may include a first sun gear and a second sungear having different numbers of teeth and a carrier arranged to hold atleast one stepped gear linking a first pinion gear engaging with thefirst sun gear to a second pinion gear engaging with the second sungear. The ‘change speed transmission assembly’ is not restricted to thetransmission 60, 60A, 60B, 100, 100A, 200, or 200A but may be anyequivalent structure including a first change speed planetary gearmechanism, a first fixation structure, a second change speed planetarygear mechanism, and a transmission state changeover structure. The firstchange speed planetary gear mechanism is constructed to have an inputelement connecting with the first element of the power distributionintegration mechanism, an output element connecting with a driveshaft,and a fixable element. The first fixation structure is configured to fixthe fixable element of the first change speed planetary gear mechanismin a non-rotatable manner and to release the fixable element in arotatable manner. The second change speed planetary gear mechanism isconstructed to have an input element connecting with the second elementof the power distribution integration mechanism, an output elementconnecting with the driveshaft, and a fixable element. The transmissionstate changeover structure is configured to enable and disable powertransmission via the second change speed planetary gear mechanism. Theabove mapping of the primary elements in the embodiment and its modifiedexamples to the primary constituents in the claims of the invention isnot restrictive in any sense but is only illustrative for concretelydescribing the mode of carrying out the invention. Namely the embodimentand its modified example discussed above are to be considered in allaspects as illustrative and not restrictive.

There may be many modifications, changes, and alterations withoutdeparting from the scope or spirit of the main characteristics of thepresent invention. The scope and spirit of the present invention areindicated by the appended claims, rather than by the foregoingdescription.

The disclose of Japanese Patent Application No. 2007-164743 filed Jun.22, 2007 including specification, drawings and claims is incorporatedherein by reference in its entirety.

1. A power output apparatus configured to output power to a driveshaft,the power output apparatus comprising: an internal combustion engine; afirst motor capable power input and power output; a second motor capablepower input and power output; an accumulator configured to transmitelectric power to and from the first motor and the second motor; a powerdistribution integration mechanism being a planetary gear mechanismincluding a first element connecting with a rotating shaft of the firstmotor, a second element connecting with a rotating shaft of the secondmotor, and a third element connecting with an engine shaft of theinternal combustion engine, and configured to allow mutuallydifferential rotations of the three elements and to have a gear ratio ofapproximately 0.5; and a change speed transmission assembly including: afirst change speed planetary gear mechanism having an input elementconnecting with the first element of the power distribution integrationmechanism, an output element connecting with the driveshaft, and afixable element and configured to allow mutually differential rotationsof the three elements; a first fixation device configured to fix thefixable element of the first change speed planetary gear mechanism in anon-rotatable manner and to release the fixable element in a rotatablemanner; a second change speed planetary gear mechanism having an inputelement connecting with the second element of the power distributionintegration mechanism, an output element connecting with the driveshaft,and a fixable element and configured to allow mutually differentialrotations of the three elements; and a transmission state changeoverdevice configured to change over a state of either one of the inputelement and the fixable element of the second change speed planetarygear mechanism and thereby enable and disable power transmission via thesecond change speed planetary gear mechanism.
 2. The power outputapparatus in accordance with claim 1, wherein the power distributionintegration mechanism is a double pinion planetary gear mechanismincluding a ring gear as the third element, a sun gear as the secondelement, and a carrier as the first element arranged to hold sets of twopinion gears engaging with each other, one of the two pinion gearsengaging with the ring gear and the other of the two pinion gearsengaging with the sun gear.
 3. The power output apparatus in accordancewith claim 1, wherein the fixable element of the second change speedplanetary gear mechanism is fixed in the non-rotatable manner, andwherein the transmission state changeover device is acoupling-decoupling device configured to couple and decouple the secondelement of the power distribution integration mechanism with and fromthe input element of the second change speed planetary gear mechanism.4. The power output apparatus in accordance with claim 3, wherein thechange speed transmission assembly further includes a coupling deviceconfigured to couple and decouple the output element with and from thefixable element of the first change speed planetary gear mechanism. 5.The power output apparatus in accordance with claim 4, wherein thechange speed transmission assembly includes one single clutchfunctioning both as the first fixation device and as the couplingdevice.
 6. The power output apparatus in accordance with claim 1,wherein the transmission state changeover device is a second fixationdevice configured to fix the fixable element of the second change speedplanetary gear mechanism in a non-rotatable manner and to release thefixable element in a rotatable manner.
 7. The power output apparatus inaccordance with claim 6, wherein the change speed transmission assemblyfurther includes a first coupling device configured to couple anddecouple the output element with and from the fixable element of thefirst change speed planetary gear mechanism, and a second couplingdevice configured to couple and decouple the output element with andfrom the fixable element of the second change speed planetary gearmechanism.
 8. The power output apparatus in accordance with claim 7,wherein the change speed transmission assembly includes one single firstclutch functioning both as the first fixation device and as the firstcoupling device and one single second clutch functioning both as thesecond fixation device and as the second coupling device.
 9. The poweroutput apparatus in accordance with claim 4, the power output apparatusfurther comprising: a third fixation device configured to fix either oneof the first element and the second element of the power distributionintegration mechanism in a non-rotatable manner.
 10. The power outputapparatus in accordance with claim 7, the power output apparatus furthercomprising: a third fixation device configured to fix either one of thefirst element and the second element of the power distributionintegration mechanism in a non-rotatable manner.
 11. The power outputapparatus in accordance with claim 1, wherein the first change speedplanetary gear mechanism is a single pinion planetary gear mechanismincluding a sun gear as the input element, a ring gear as the fixableelement, and a carrier as the output element arranged to hold piniongears respectively engaging with both the sun gear and the ring gear,and wherein the second change speed planetary gear mechanism is a singlepinion planetary gear mechanism including a ring gear as the inputelement, a sun gear as the fixable element, and a carrier as the outputelement arranged to hold pinion gears respectively engaging with boththe ring gear and the sun gear.
 12. The power output apparatus inaccordance with claim 11, wherein the sun gear of the second changespeed planetary gear mechanism is attached to a hollow sun gear shaft,and wherein the ring gear of the second change speed planetary gearmechanism is connected with the second element of the power distributionintegration mechanism via a shaft located in and passed through thehollow sun gear shaft.
 13. The power output apparatus in accordance withclaim 11, wherein the sun gear of the second change speed planetary gearmechanism is attached to a hollow sun gear shaft, and wherein thecarrier of the second change speed planetary gear mechanism is connectedwith driveshaft via a shaft located in and passed through the hollow sungear shaft.
 14. The power output apparatus in accordance with claim 1,wherein the first change speed planetary gear mechanism is a singlepinion planetary gear mechanism including a sun gear as the inputelement, a ring gear as the fixable elements and a carrier as the outputelement arranged to hold pinion gears respectively engaging with boththe sun gear and the ring gear, and wherein the second change speedplanetary gear mechanism is a planetary gear mechanism including a firstsun gear as the input element, a second sun gear as the output elementhaving a different number of teeth from that of the first sun gear andconnected with the carrier of the first change speed planetary gearmechanism and with the driveshaft, and a carrier as the fixable elementarranged to hold a stepped gear of linking a first pinion gear engagingwith the first sun gear to a second pinion gear engaging with the secondsun gear.
 15. The power output apparatus in accordance with claim 1,wherein the first change speed planetary gear mechanism is a singlepinion planetary gear mechanism including a sun gear as the inputelement, a ring gear as the fixable element, and a carrier as the outputelement arranged to hold pinion gears respectively engaging with boththe sun gear and the ring gear, and wherein the second change speedplanetary gear mechanism is a double pinion planetary gear mechanismincluding a sun gear as the input element, a ring gear as the outputelement, and a carrier as the fixable element arranged to hold sets oftwo pinion gears engaging with each other, one of the two pinion gearsengaging with the sun gear and the other of the two pinion gearsengaging with the ring gear.
 16. A hybrid vehicle with drive wheelsdriven by means of power from a driveshaft, the hybrid vehiclecomprising: an internal combustion engine; a first motor capable powerinput and power output; a second motor capable power input and poweroutput; an accumulator configured to transmit electric power to and fromthe first motor and the second motor; a power distribution integrationmechanism being a planetary gear mechanism including a first elementconnecting with a rotating shaft of the first motor, a second elementconnecting with a rotating shaft of the second motor, and a thirdelement connecting with an engine shaft of the internal combustionengine, and configured to allow mutually differential rotations of thethree elements and to have a gear ratio of approximately 0.5; and achange speed transmission assembly including: a first change speedplanetary gear mechanism having an input element connecting with thefirst element of the power distribution integration mechanism, an outputelement connecting with the driveshaft, and a fixable element andconfigured to allow mutually differential rotations of the threeelements; a first fixation device configured to fix the fixable elementof the first change speed planetary gear mechanism in a non-rotatablemanner and to release the fixable element in a rotatable manner; asecond change speed planetary gear mechanism having an input elementconnecting with the second element of the power distribution integrationmechanism, an output element connecting with the driveshaft, and afixable element and configured to allow mutually differential rotationsof the three elements; and a transmission state changeover deviceconfigured to change over a state of either one of the input element andthe fixable element of the second change speed planetary gear mechanismand thereby enable and disable power transmission via the second changespeed planetary gear mechanism.